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Operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer from cellular phones and video game consoles to web servers and supercomputers. The dominant general-purpose personal computer operating system is Microsoft Windows with a market share of around 76.45%. macOS by Apple Inc. is in second place (17.72%), and the varieties of Linux are collectively in third place (1.73%). In the mobile sector (including smartphones and tablets), Android's share is up to 72% in the year 2020. According to third quarter 2016 data, Android's share on smartphones is dominant with 87.5 percent with also a growth rate of 10.3 percent per year, followed by Apple's iOS with 12.1 percent with per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent. Linux distributions are dominant in the server and supercomputing sectors. Other specialized classes of operating systems (special-purpose operating systems), such as embedded and real-time systems, exist for many applications. Security-focused operating systems also exist. Some operating systems have low system requirements (e.g. light-weight Linux distribution). Others may have higher system requirements. Some operating systems require installation or may come pre-installed with purchased computers (OEM-installation), whereas others may run directly from media (i.e. live CD) or flash memory (i.e. USB stick). Types of operating systems Single-tasking and multi-tasking A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency. This is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted repeatedly in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in preemptive and co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, such as Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking; 32-bit versions of both Windows NT and Win9x used preemptive multi-tasking. Single- and multi-user Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, and the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources to multiple users. Distributed A distributed operating system manages a group of distinct, networked computers and makes them appear to be a single computer, as all computations are distributed (divided amongst the constituent computers). Templated In the distributed and cloud computing context of an OS, templating refers to creating a single virtual machine image as a guest operating system, then saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, and is common in large server warehouses. Embedded Embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines with less autonomy (e.g. PDAs). They are very compact and extremely efficient by design, and are able to operate with a limited amount of resources. Windows CE and Minix 3 are some examples of embedded operating systems. Real-time A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. Such an event-driven system switches between tasks based on their priorities or external events, whereas time-sharing operating systems switch tasks based on clock interrupts. Library A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. History Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their modern and more complex forms until the early 1960s. Hardware features were added, that enabled use of runtime libraries, interrupts, and parallel processing. When personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems. Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plugboards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the printing of payroll checks from data on punched paper cards. After programmable general-purpose computers were invented, machine languages(consisting of strings of the binary digits 0 and 1 on punched paper tape) were introduced that sped up the programming process (Stern, 1981). In the early 1950s, a computer could execute only one program at a time. Each user had sole use of the computer for a limited period and would arrive at a scheduled time with their program and data on punched paper cards or punched tape. The program would be loaded into the machine, and the machine would be set to work until the program completed or crashed. Programs could generally be debugged via a front panel using toggle switches and panel lights. It is said that Alan Turing was a master of this on the early Manchester Mark 1 machine, and he was already deriving the primitive conception of an operating system from the principles of the universal Turing machine. Later machines came with libraries of programs, which would be linked to a user's program to assist in operations such as input and output and compiling (generating machine code from human-readable symbolic code). This was the genesis of the modern-day operating system. However, machines still ran a single job at a time. At Cambridge University in England, the job queue was at one time a washing line (clothesline) from which tapes were hung with different colored clothes-pegs to indicate job priority. An improvement was the Atlas Supervisor. Introduced with the Manchester Atlas in 1962, it is considered by many to be the first recognisable modern operating system. Brinch Hansen described it as "the most significant breakthrough in the history of operating systems." Mainframes Through the 1950s, many major features were pioneered in the field of operating systems on mainframe computers, including batch processing, input/output interrupting, buffering, multitasking, spooling, runtime libraries, link-loading, and programs for sorting records in files. These features were included or not included in application software at the option of application programmers, rather than in a separate operating system used by all applications. In 1959, the SHARE Operating System was released as an integrated utility for the IBM 704, and later in the 709 and 7090 mainframes, although it was quickly supplanted by IBSYS/IBJOB on the 709, 7090 and 7094. During the 1960s, IBM's OS/360 introduced the concept of a single OS spanning an entire product line, which was crucial for the success of the System/360 machines. IBM's current mainframe operating systems are distant descendants of this original system and modern machines are backwards-compatible with applications written for OS/360. OS/360 also pioneered the concept that the operating system keeps track of all of the system resources that are used, including program and data space allocation in main memory and file space in secondary storage, and file locking during updates. When a process is terminated for any reason, all of these resources are re-claimed by the operating system. The alternative CP-67 system for the S/360-67 started a whole line of IBM operating systems focused on the concept of virtual machines. Other operating systems used on IBM S/360 series mainframes included systems developed by IBM: DOS/360 (Disk Operating System), TSS/360 (Time Sharing System), TOS/360 (Tape Operating System), BOS/360 (Basic Operating System), and ACP (Airline Control Program), as well as a few non-IBM systems: MTS (Michigan Terminal System), MUSIC (Multi-User System for Interactive Computing), and ORVYL (Stanford Timesharing System). Control Data Corporation developed the SCOPE operating system in the 1960s, for batch processing. In cooperation with the University of Minnesota, the Kronos and later the NOS operating systems were developed during the 1970s, which supported simultaneous batch and timesharing use. Like many commercial timesharing systems, its interface was an extension of the Dartmouth BASIC operating systems, one of the pioneering efforts in timesharing and programming languages. In the late 1970s, Control Data and the University of Illinois developed the PLATO operating system, which used plasma panel displays and long-distance time sharing networks. Plato was remarkably innovative for its time, featuring real-time chat, and multi-user graphical games. In 1961, Burroughs Corporation introduced the B5000 with the MCP (Master Control Program) operating system. The B5000 was a stack machine designed to exclusively support high-level languages with no assembler; indeed, the MCP was the first OS to be written exclusively in a high-level language (ESPOL, a dialect of ALGOL). MCP also introduced many other ground-breaking innovations, such as being the first commercial implementation of virtual memory. During development of the AS/400, IBM made an approach to Burroughs to license MCP to run on the AS/400 hardware. This proposal was declined by Burroughs management to protect its existing hardware production. MCP is still in use today in the Unisys company's MCP/ClearPath line of computers. UNIVAC, the first commercial computer manufacturer, produced a series of EXEC operating systems. Like all early main-frame systems, this batch-oriented system managed magnetic drums, disks, card readers and line printers. In the 1970s, UNIVAC produced the Real-Time Basic (RTB) system to support large-scale time sharing, also patterned after the Dartmouth BC system. General Electric and MIT developed General Electric Comprehensive Operating Supervisor (GECOS), which introduced the concept of ringed security privilege levels. After acquisition by Honeywell it was renamed General Comprehensive Operating System (GCOS). Digital Equipment Corporation developed many operating systems for its various computer lines, including TOPS-10 and TOPS-20 time sharing systems for the 36-bit PDP-10 class systems. Before the widespread use of UNIX, TOPS-10 was a particularly popular system in universities, and in the early ARPANET community. RT-11 was a single-user real-time OS for the PDP-11 class minicomputer, and RSX-11 was the corresponding multi-user OS. From the late 1960s through the late 1970s, several hardware capabilities evolved that allowed similar or ported software to run on more than one system. Early systems had utilized microprogramming to implement features on their systems in order to permit different underlying computer architectures to appear to be the same as others in a series. In fact, most 360s after the 360/40 (except the 360/44, 360/75, 360/91, 360/95 and 360/195) were microprogrammed implementations. The enormous investment in software for these systems made since the 1960s caused most of the original computer manufacturers to continue to develop compatible operating systems along with the hardware. Notable supported mainframe operating systems include: Burroughs MCP B5000, 1961 to Unisys Clearpath/MCP, present IBM OS/360 IBM System/360, 1966 to IBM z/OS, present IBM CP-67 IBM System/360, 1967 to IBM z/VM UNIVAC EXEC 8 UNIVAC 1108, 1967, to OS 2200 Unisys Clearpath Dorado, present Microcomputers The first microcomputers did not have the capacity or need for the elaborate operating systems that had been developed for mainframes and minis; minimalistic operating systems were developed, often loaded from ROM and known as monitors. One notable early disk operating system was CP/M, which was supported on many early microcomputers and was closely imitated by Microsoft's MS-DOS, which became widely popular as the operating system chosen for the IBM PC (IBM's version of it was called IBM DOS or PC DOS). In the 1980s, Apple Computer Inc. (now Apple Inc.) abandoned its popular Apple II series of microcomputers to introduce the Apple Macintosh computer with an innovative graphical user interface (GUI) to the Mac OS. The introduction of the Intel 80386 CPU chip in October 1985, with 32-bit architecture and paging capabilities, provided personal computers with the ability to run multitasking operating systems like those of earlier minicomputers and mainframes. Microsoft responded to this progress by hiring Dave Cutler, who had developed the VMS operating system for Digital Equipment Corporation. He would lead the development of the Windows NT operating system, which continues to serve as the basis for Microsoft's operating systems line. Steve Jobs, a co-founder of Apple Inc., started NeXT Computer Inc., which developed the NEXTSTEP operating system. NEXTSTEP would later be acquired by Apple Inc. and used, along with code from FreeBSD as the core of Mac OS X (macOS after latest name change). The GNU Project was started by activist and programmer Richard Stallman with the goal of creating a complete free software replacement to the proprietary UNIX operating system. While the project was highly successful in duplicating the functionality of various parts of UNIX, development of the GNU Hurd kernel proved to be unproductive. In 1991, Finnish computer science student Linus Torvalds, with cooperation from volunteers collaborating over the Internet, released the first version of the Linux kernel. It was soon merged with the GNU user space components and system software to form a complete operating system. Since then, the combination of the two major components has usually been referred to as simply "Linux" by the software industry, a naming convention that Stallman and the Free Software Foundation remain opposed to, preferring the name GNU/Linux. The Berkeley Software Distribution, known as BSD, is the UNIX derivative distributed by the University of California, Berkeley, starting in the 1970s. Freely distributed and ported to many minicomputers, it eventually also gained a following for use on PCs, mainly as FreeBSD, NetBSD and OpenBSD. Examples Unix and Unix-like operating systems Unix was originally written in assembly language. Ken Thompson wrote B, mainly based on BCPL, based on his experience in the MULTICS project. B was replaced by C, and Unix, rewritten in C, developed into a large, complex family of inter-related operating systems which have been influential in every modern operating system (see History). The Unix-like family is a diverse group of operating systems, with several major sub-categories including System V, BSD, and Linux. The name "UNIX" is a trademark of The Open Group which licenses it for use with any operating system that has been shown to conform to their definitions. "UNIX-like" is commonly used to refer to the large set of operating systems which resemble the original UNIX. Unix-like systems run on a wide variety of computer architectures. They are used heavily for servers in business, as well as workstations in academic and engineering environments. Free UNIX variants, such as Linux and BSD, are popular in these areas. Five operating systems are certified by The Open Group (holder of the Unix trademark) as Unix. HP's HP-UX and IBM's AIX are both descendants of the original System V Unix and are designed to run only on their respective vendor's hardware. In contrast, Sun Microsystems's Solaris can run on multiple types of hardware, including x86 and Sparc servers, and PCs. Apple's macOS, a replacement for Apple's earlier (non-Unix) Mac OS, is a hybrid kernel-based BSD variant derived from NeXTSTEP, Mach, and FreeBSD. IBM's z/OS UNIX System Services includes a shell and utilities based on Mortice Kerns' InterOpen products. Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants. BSD and its descendants A subgroup of the Unix family is the Berkeley Software Distribution family, which includes FreeBSD, NetBSD, and OpenBSD. These operating systems are most commonly found on webservers, although they can also function as a personal computer OS. The Internet owes much of its existence to BSD, as many of the protocols now commonly used by computers to connect, send and receive data over a network were widely implemented and refined in BSD. The World Wide Web was also first demonstrated on a number of computers running an OS based on BSD called NeXTSTEP. In 1974, University of California, Berkeley installed its first Unix system. Over time, students and staff in the computer science department there began adding new programs to make things easier, such as text editors. When Berkeley received new VAX computers in 1978 with Unix installed, the school's undergraduates modified Unix even more in order to take advantage of the computer's hardware possibilities. The Defense Advanced Research Projects Agency of the US Department of Defense took interest, and decided to fund the project. Many schools, corporations, and government organizations took notice and started to use Berkeley's version of Unix instead of the official one distributed by AT&T. Steve Jobs, upon leaving Apple Inc. in 1985, formed NeXT Inc., a company that manufactured high-end computers running on a variation of BSD called NeXTSTEP. One of these computers was used by Tim Berners-Lee as the first webserver to create the World Wide Web. Developers like Keith Bostic encouraged the project to replace any non-free code that originated with Bell Labs. Once this was done, however, AT&T sued. After two years of legal disputes, the BSD project spawned a number of free derivatives, such as NetBSD and FreeBSD (both in 1993), and OpenBSD (from NetBSD in 1995). macOS macOS (formerly "Mac OS X" and later "OS X") is a line of open core graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. macOS is the successor to the original classic Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessor, macOS is a UNIX operating system built on technology that had been developed at NeXT through the second half of the 1980s and up until Apple purchased the company in early 1997. The operating system was first released in 1999 as Mac OS X Server 1.0, followed in March 2001 by a client version (Mac OS X v10.0 "Cheetah"). Since then, six more distinct "client" and "server" editions of macOS have been released, until the two were merged in OS X 10.7 "Lion". Prior to its merging with macOS, the server edition macOS Server was architecturally identical to its desktop counterpart and usually ran on Apple's line of Macintosh server hardware. macOS Server included work group management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others. With Mac OS X v10.7 Lion, all server aspects of Mac OS X Server have been integrated into the client version and the product re-branded as "OS X" (dropping "Mac" from the name). The server tools are now offered as an application. z/OS UNIX System Services First introduced as the OpenEdition upgrade to MVS/ESA System Product Version 4 Release 3, announced February 1993 with support for POSIX and other standards., z/OS UNIX System Services is built on top of MVS services and cannot run independently. While IBM initially introduced OpenEdition to satisfy FIPS requirements, several z/OS component now require UNIX services, e.g., TCP/IP. Linux The Linux kernel originated in 1991, as a project of Linus Torvalds, while a university student in Finland. He posted information about his project on a newsgroup for computer students and programmers, and received support and assistance from volunteers who succeeded in creating a complete and functional kernel. Linux is Unix-like, but was developed without any Unix code, unlike BSD and its variants. Because of its open license model, the Linux kernel code is available for study and modification, which resulted in its use on a wide range of computing machinery from supercomputers to smart-watches. Although estimates suggest that Linux is used on only 1.82% of all "desktop" (or laptop) PCs, it has been widely adopted for use in servers and embedded systems such as cell phones. Linux has superseded Unix on many platforms and is used on most supercomputers including the top 385. Many of the same computers are also on Green500 (but in different order), and Linux runs on the top 10. Linux is also commonly used on other small energy-efficient computers, such as smartphones and smartwatches. The Linux kernel is used in some popular distributions, such as Red Hat, Debian, Ubuntu, Linux Mint and Google's Android, Chrome OS, and Chromium OS. Microsoft Windows Microsoft Windows is a family of proprietary operating systems designed by Microsoft Corporation and primarily targeted to Intel architecture based computers, with an estimated 88.9 percent total usage share on Web connected computers. The latest version is Windows 11. In 2011, Windows 7 overtook Windows XP as most common version in use. Microsoft Windows was first released in 1985, as an operating environment running on top of MS-DOS, which was the standard operating system shipped on most Intel architecture personal computers at the time. In 1995, Windows 95 was released which only used MS-DOS as a bootstrap. For backwards compatibility, Win9x could run real-mode MS-DOS and 16-bit Windows 3.x drivers. Windows ME, released in 2000, was the last version in the Win9x family. Later versions have all been based on the Windows NT kernel. Current client versions of Windows run on IA-32, x86-64 and ARM microprocessors. In addition Itanium is still supported in older server version Windows Server 2008 R2. In the past, Windows NT supported additional architectures. Server editions of Windows are widely used. In recent years, Microsoft has expended significant capital in an effort to promote the use of Windows as a server operating system. However, Windows' usage on servers is not as widespread as on personal computers as Windows competes against Linux and BSD for server market share. ReactOS is a Windows-alternative operating system, which is being developed on the principles of Windows without using any of Microsoft's code. Other There have been many operating systems that were significant in their day but are no longer so, such as AmigaOS; OS/2 from IBM and Microsoft; classic Mac OS, the non-Unix precursor to Apple's macOS; BeOS; XTS-300; RISC OS; MorphOS; Haiku; BareMetal and FreeMint. Some are still used in niche markets and continue to be developed as minority platforms for enthusiast communities and specialist applications. OpenVMS, formerly from DEC, is still under active development by VMS Software Inc. Yet other operating systems are used almost exclusively in academia, for operating systems education or to do research on operating system concepts. A typical example of a system that fulfills both roles is MINIX, while for example Singularity is used purely for research. Another example is the Oberon System designed at ETH Zürich by Niklaus Wirth, Jürg Gutknecht and a group of students at the former Computer Systems Institute in the 1980s. It was used mainly for research, teaching, and daily work in Wirth's group. Other operating systems have failed to win significant market share, but have introduced innovations that have influenced mainstream operating systems, not least Bell Labs' Plan 9. Components The components of an operating system all exist in order to make the different parts of a computer work together. All user software needs to go through the operating system in order to use any of the hardware, whether it be as simple as a mouse or keyboard or as complex as an Internet component. Kernel With the aid of the firmware and device drivers, the kernel provides the most basic level of control over all of the computer's hardware devices. It manages memory access for programs in the RAM, it determines which programs get access to which hardware resources, it sets up or resets the CPU's operating states for optimal operation at all times, and it organizes the data for long-term non-volatile storage with file systems on such media as disks, tapes, flash memory, etc. Program execution The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with the hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs. Executing an application program involves the creation of a process by the operating system kernel which assigns memory space and other resources, establishes a priority for the process in multi-tasking systems, loads program binary code into memory, and initiates execution of the application program which then interacts with the user and with hardware devices. Interrupts Interrupts are central to most operating systems, as they provide an efficient way to react to the environment. Interrupts cause the central processing unit (CPU) to have a control flow change away from the currently running process. Input/Output (I/O) devices are slower than the CPU's clock signal. Therefore, it would slow down the computer if the CPU had to wait for each I/O to finish. Instead, a computer may implement direct memory access (DMA) I/O. The details of how a computer processes an interrupt vary from architecture to architecture, and the details of how interrupt service routines behave from operating system to operating system. The scenario below is typical, although the details for some other hardware and operating systems vary significantly. If a computer program in a computer with a direct memory access chip executes a system call to perform a DMA I/O blocking write operation, then the system call might execute the following instructions: Set the contents of the CPU's registers (including the program counter) into the process control block. Create an entry in the device-status table. The operating system maintains this table to keep track of which processes are waiting for which devices. One field in the table is the memory address of the process control block. Place all the characters to be sent to the device into a memory buffer. Set the memory address of the memory buffer to a predetermined device register. Set the buffer size (an integer) to another predetermined register. Execute the machine instruction to begin the writing. Perform a context switch to the next process in the ready queue. While the writing takes place, the operating system will context switch to other processes as normal. When the device finishes writing, the device will interrupt the currently running process by asserting an interrupt request. The device will also place an integer onto the device's data bus. Upon accepting the interrupt request, the CPU will: Push the contents of its program counter and program status word onto the call stack. Read the integer from the data bus. The integer is an offset to the interrupt vector table. The vector table's instructions will return control to the operating system. The operating system will then: Access the device-status table. Extract the process control block. Perform a context switch back to the writing process. When the writing process has its time slice expired, the CPU will: Pop from the call stack the program status word and set it back to its register. Pop from the call stack the address of the interrupted process' next instruction and set it back into the program counter. The interrupted process will then resume its time slice. Modes Modern computers support multiple modes of operation. CPUs with this capability offer at least two modes: user mode and supervisor mode. In general terms, supervisor mode operation allows unrestricted access to all machine resources, including all MPU instructions. User mode operation sets limits on instruction use and typically disallows direct access to machine resources. CPUs might have other modes similar to user mode as well, such as the virtual modes in order to emulate older processor types, such as 16-bit processors on a 32-bit one, or 32-bit processors on a 64-bit one. At power-on or reset, the system begins in supervisor mode. Once an operating system kernel has been loaded and started, the boundary between user mode and supervisor mode (also known as kernel mode) can be established. Supervisor mode is used by the kernel for low level tasks that need unrestricted access to hardware, such as controlling how memory is accessed, and communicating with devices such as disk drives and video display devices. User mode, in contrast, is used for almost everything else. Application programs, such as word processors and database managers, operate within user mode, and can only access machine resources by turning control over to the kernel, a process which causes a switch to supervisor mode. Typically, the transfer of control to the kernel is achieved by executing a software interrupt instruction, such as the Motorola 68000 TRAP instruction. The software interrupt causes the processor to switch from user mode to supervisor mode and begin executing code that allows the kernel to take control. In user mode, programs usually have access to a restricted set of processor instructions, and generally cannot execute any instructions that could potentially cause disruption to the system's operation. In supervisor mode, instruction execution restrictions are typically removed, allowing the kernel unrestricted access to all machine resources. The term "user mode resource" generally refers to one or more CPU registers, which contain information that the running program isn't allowed to alter. Attempts to alter these resources generally causes a switch to supervisor mode, where the operating system can deal with the illegal operation the program was attempting, for example, by forcibly terminating ("killing") the program. Memory management Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by programs. This ensures that a program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory. Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If a program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system. Memory protection enables the kernel to limit a process' access to the computer's memory. Various methods of memory protection exist, including memory segmentation and paging. All methods require some level of hardware support (such as the 80286 MMU), which doesn't exist in all computers. In both segmentation and paging, certain protected mode registers specify to the CPU what memory address it should allow a running program to access. Attempts to access other addresses trigger an interrupt which cause the CPU to re-enter supervisor mode, placing the kernel in charge. This is called a segmentation violation or Seg-V for short, and since it is both difficult to assign a meaningful result to such an operation, and because it is usually a sign of a misbehaving program, the kernel generally resorts to terminating the offending program, and reports the error. Windows versions 3.1 through ME had some level of memory protection, but programs could easily circumvent the need to use it. A general protection fault would be produced, indicating a segmentation violation had occurred; however, the system would often crash anyway. Virtual memory The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks. If a program tries to access memory that isn't in its current range of accessible memory, but nonetheless has been allocated to it, the kernel is interrupted in the same way as it would if the program were to exceed its allocated memory. (See section on memory management.) Under UNIX this kind of interrupt is referred to as a page fault. When the kernel detects a page fault it generally adjusts the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where a particular application's memory is stored, or even whether or not it has actually been allocated yet. In modern operating systems, memory which is accessed less frequently can be temporarily stored on disk or other media to make that space available for use by other programs. This is called swapping, as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand. "Virtual memory" provides the programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there. Multitasking Multitasking refers to the running of multiple independent computer programs on the same computer; giving the appearance that it is performing the tasks at the same time. Since most computers can do at most one or two things at one time, this is generally done via time-sharing, which means that each program uses a share of the computer's time to execute. An operating system kernel contains a scheduling program which determines how much time each process spends executing, and in which order execution control should be passed to programs. Control is passed to a process by the kernel, which allows the program access to the CPU and memory. Later, control is returned to the kernel through some mechanism, so that another program may be allowed to use the CPU. This so-called passing of control between the kernel and applications is called a context switch. An early model which governed the allocation of time to programs was called cooperative multitasking. In this model, when control is passed to a program by the kernel, it may execute for as long as it wants before explicitly returning control to the kernel. This means that a malicious or malfunctioning program may not only prevent any other programs from using the CPU, but it can hang the entire system if it enters an infinite loop. Modern operating systems extend the concepts of application preemption to device drivers and kernel code, so that the operating system has preemptive control over internal run-times as well. The philosophy governing preemptive multitasking is that of ensuring that all programs are given regular time on the CPU. This implies that all programs must be limited in how much time they are allowed to spend on the CPU without being interrupted. To accomplish this, modern operating system kernels make use of a timed interrupt. A protected mode timer is set by the kernel which triggers a return to supervisor mode after the specified time has elapsed. (See above sections on Interrupts and Dual Mode Operation.) On many single user operating systems cooperative multitasking is perfectly adequate, as home computers generally run a small number of well tested programs. The AmigaOS is an exception, having preemptive multitasking from its first version. Windows NT was the first version of Microsoft Windows which enforced preemptive multitasking, but it didn't reach the home user market until Windows XP (since Windows NT was targeted at professionals). Disk access and file systems Access to data stored on disks is a central feature of all operating systems. Computers store data on disks using files, which are structured in specific ways in order to allow for faster access, higher reliability, and to make better use of the drive's available space. The specific way in which files are stored on a disk is called a file system, and enables files to have names and attributes. It also allows them to be stored in a hierarchy of directories or folders arranged in a directory tree. Early operating systems generally supported a single type of disk drive and only one kind of file system. Early file systems were limited in their capacity, speed, and in the kinds of file names and directory structures they could use. These limitations often reflected limitations in the operating systems they were designed for, making it very difficult for an operating system to support more than one file system. While many simpler operating systems support a limited range of options for accessing storage systems, operating systems like UNIX and Linux support a technology known as a virtual file system or VFS. An operating system such as UNIX supports a wide array of storage devices, regardless of their design or file systems, allowing them to be accessed through a common application programming interface (API). This makes it unnecessary for programs to have any knowledge about the device they are accessing. A VFS allows the operating system to provide programs with access to an unlimited number of devices with an infinite variety of file systems installed on them, through the use of specific device drivers and file system drivers. A connected storage device, such as a hard drive, is accessed through a device driver. The device driver understands the specific language of the drive and is able to translate that language into a standard language used by the operating system to access all disk drives. On UNIX, this is the language of block devices. When the kernel has an appropriate device driver in place, it can then access the contents of the disk drive in raw format, which may contain one or more file systems. A file system driver is used to translate the commands used to access each specific file system into a standard set of commands that the operating system can use to talk to all file systems. Programs can then deal with these file systems on the basis of filenames, and directories/folders, contained within a hierarchical structure. They can create, delete, open, and close files, as well as gather various information about them, including access permissions, size, free space, and creation and modification dates. Various differences between file systems make supporting all file systems difficult. Allowed characters in file names, case sensitivity, and the presence of various kinds of file attributes makes the implementation of a single interface for every file system a daunting task. Operating systems tend to recommend using (and so support natively) file systems specifically designed for them; for example, NTFS in Windows and ReiserFS, Reiser4, ext3, ext4 and Btrfs in Linux. However, in practice, third party drivers are usually available to give support for the most widely used file systems in most general-purpose operating systems (for example, NTFS is available in Linux through NTFS-3g, and ext2/3 and ReiserFS are available in Windows through third-party software). Support for file systems is highly varied among modern operating systems, although there are several common file systems which almost all operating systems include support and drivers for. Operating systems vary on file system support and on the disk formats they may be installed on. Under Windows, each file system is usually limited in application to certain media; for example, CDs must use ISO 9660 or UDF, and as of Windows Vista, NTFS is the only file system which the operating system can be installed on. It is possible to install Linux onto many types of file systems. Unlike other operating systems, Linux and UNIX allow any file system to be used regardless of the media it is stored in, whether it is a hard drive, a disc (CD, DVD...), a USB flash drive, or even contained within a file located on another file system. Device drivers A device driver is a specific type of computer software developed to allow interaction with hardware devices. Typically this constitutes an interface for communicating with the device, through the specific computer bus or communications subsystem that the hardware is connected to, providing commands to and/or receiving data from the device, and on the other end, the requisite interfaces to the operating system and software applications. It is a specialized hardware-dependent computer program which is also operating system specific that enables another program, typically an operating system or applications software package or computer program running under the operating system kernel, to interact transparently with a hardware device, and usually provides the requisite interrupt handling necessary for any necessary asynchronous time-dependent hardware interfacing needs. The key design goal of device drivers is abstraction. Every model of hardware (even within the same class of device) is different. Newer models also are released by manufacturers that provide more reliable or better performance and these newer models are often controlled differently. Computers and their operating systems cannot be expected to know how to control every device, both now and in the future. To solve this problem, operating systems essentially dictate how every type of device should be controlled. The function of the device driver is then to translate these operating system mandated function calls into device specific calls. In theory a new device, which is controlled in a new manner, should function correctly if a suitable driver is available. This new driver ensures that the device appears to operate as usual from the operating system's point of view. Under versions of Windows before Vista and versions of Linux before 2.6, all driver execution was co-operative, meaning that if a driver entered an infinite loop it would freeze the system. More recent revisions of these operating systems incorporate kernel preemption, where the kernel interrupts the driver to give it tasks, and then separates itself from the process until it receives a response from the device driver, or gives it more tasks to do. Networking Currently most operating systems support a variety of networking protocols, hardware, and applications for using them. This means that computers running dissimilar operating systems can participate in a common network for sharing resources such as computing, files, printers, and scanners using either wired or wireless connections. Networks can essentially allow a computer's operating system to access the resources of a remote computer to support the same functions as it could if those resources were connected directly to the local computer. This includes everything from simple communication, to using networked file systems or even sharing another computer's graphics or sound hardware. Some network services allow the resources of a computer to be accessed transparently, such as SSH which allows networked users direct access to a computer's command line interface. Client/server networking allows a program on a computer, called a client, to connect via a network to another computer, called a server. Servers offer (or host) various services to other network computers and users. These services are usually provided through ports or numbered access points beyond the server's IP address. Each port number is usually associated with a maximum of one running program, which is responsible for handling requests to that port. A daemon, being a user program, can in turn access the local hardware resources of that computer by passing requests to the operating system kernel. Many operating systems support one or more vendor-specific or open networking protocols as well, for example, SNA on IBM systems, DECnet on systems from Digital Equipment Corporation, and Microsoft-specific protocols (SMB) on Windows. Specific protocols for specific tasks may also be supported such as NFS for file access. Protocols like ESound, or esd can be easily extended over the network to provide sound from local applications, on a remote system's sound hardware. Security A computer being secure depends on a number of technologies working properly. A modern operating system provides access to a number of resources, which are available to software running on the system, and to external devices like networks via the kernel. The operating system must be capable of distinguishing between requests which should be allowed to be processed, and others which should not be processed. While some systems may simply distinguish between "privileged" and "non-privileged", systems commonly have a form of requester identity, such as a user name. To establish identity there may be a process of authentication. Often a username must be quoted, and each username may have a password. Other methods of authentication, such as magnetic cards or biometric data, might be used instead. In some cases, especially connections from the network, resources may be accessed with no authentication at all (such as reading files over a network share). Also covered by the concept of requester identity is authorization; the particular services and resources accessible by the requester once logged into a system are tied to either the requester's user account or to the variously configured groups of users to which the requester belongs. In addition to the allow or disallow model of security, a system with a high level of security also offers auditing options. These would allow tracking of requests for access to resources (such as, "who has been reading this file?"). Internal security, or security from an already running program is only possible if all possibly harmful requests must be carried out through interrupts to the operating system kernel. If programs can directly access hardware and resources, they cannot be secured. External security involves a request from outside the computer, such as a login at a connected console or some kind of network connection. External requests are often passed through device drivers to the operating system's kernel, where they can be passed onto applications, or carried out directly. Security of operating systems has long been a concern because of highly sensitive data held on computers, both of a commercial and military nature. The United States Government Department of Defense (DoD) created the Trusted Computer System Evaluation Criteria (TCSEC) which is a standard that sets basic requirements for assessing the effectiveness of security. This became of vital importance to operating system makers, because the TCSEC was used to evaluate, classify and select trusted operating systems being considered for the processing, storage and retrieval of sensitive or classified information. Network services include offerings such as file sharing, print services, email, web sites, and file transfer protocols (FTP), most of which can have compromised security. At the front line of security are hardware devices known as firewalls or intrusion detection/prevention systems. At the operating system level, there are a number of software firewalls available, as well as intrusion detection/prevention systems. Most modern operating systems include a software firewall, which is enabled by default. A software firewall can be configured to allow or deny network traffic to or from a service or application running on the operating system. Therefore, one can install and be running an insecure service, such as Telnet or FTP, and not have to be threatened by a security breach because the firewall would deny all traffic trying to connect to the service on that port. An alternative strategy, and the only sandbox strategy available in systems that do not meet the Popek and Goldberg virtualization requirements, is where the operating system is not running user programs as native code, but instead either emulates a processor or provides a host for a p-code based system such as Java. Internal security is especially relevant for multi-user systems; it allows each user of the system to have private files that the other users cannot tamper with or read. Internal security is also vital if auditing is to be of any use, since a program can potentially bypass the operating system, inclusive of bypassing auditing. User interface Every computer that is to be operated by an individual requires a user interface. The user interface is usually referred to as a shell and is essential if human interaction is to be supported. The user interface views the directory structure and requests services from the operating system that will acquire data from input hardware devices, such as a keyboard, mouse or credit card reader, and requests operating system services to display prompts, status messages and such on output hardware devices, such as a video monitor or printer. The two most common forms of a user interface have historically been the command-line interface, where computer commands are typed out line-by-line, and the graphical user interface, where a visual environment (most commonly a WIMP) is present. Graphical user interfaces Most of the modern computer systems support graphical user interfaces (GUI), and often include them. In some computer systems, such as the original implementation of the classic Mac OS, the GUI is integrated into the kernel. While technically a graphical user interface is not an operating system service, incorporating support for one into the operating system kernel can allow the GUI to be more responsive by reducing the number of context switches required for the GUI to perform its output functions. Other operating systems are modular, separating the graphics subsystem from the kernel and the Operating System. In the 1980s UNIX, VMS and many others had operating systems that were built this way. Linux and macOS are also built this way. Modern releases of Microsoft Windows such as Windows Vista implement a graphics subsystem that is mostly in user-space; however the graphics drawing routines of versions between Windows NT 4.0 and Windows Server 2003 exist mostly in kernel space. Windows 9x had very little distinction between the interface and the kernel. Many computer operating systems allow the user to install or create any user interface they desire. The X Window System in conjunction with GNOME or KDE Plasma 5 is a commonly found setup on most Unix and Unix-like (BSD, Linux, Solaris) systems. A number of Windows shell replacements have been released for Microsoft Windows, which offer alternatives to the included Windows shell, but the shell itself cannot be separated from Windows. Numerous Unix-based GUIs have existed over time, most derived from X11. Competition among the various vendors of Unix (HP, IBM, Sun) led to much fragmentation, though an effort to standardize in the 1990s to COSE and CDE failed for various reasons, and were eventually eclipsed by the widespread adoption of GNOME and K Desktop Environment. Prior to free software-based toolkits and desktop environments, Motif was the prevalent toolkit/desktop combination (and was the basis upon which CDE was developed). Graphical user interfaces evolve over time. For example, Windows has modified its user interface almost every time a new major version of Windows is released, and the Mac OS GUI changed dramatically with the introduction of Mac OS X in 1999. Real-time operating systems A real-time operating system (RTOS) is an operating system intended for applications with fixed deadlines (real-time computing). Such applications include some small embedded systems, automobile engine controllers, industrial robots, spacecraft, industrial control, and some large-scale computing systems. An early example of a large-scale real-time operating system was Transaction Processing Facility developed by American Airlines and IBM for the Sabre Airline Reservations System. Embedded systems that have fixed deadlines use a real-time operating system such as VxWorks, PikeOS, eCos, QNX, MontaVista Linux and RTLinux. Windows CE is a real-time operating system that shares similar APIs to desktop Windows but shares none of desktop Windows' codebase. Symbian OS also has an RTOS kernel (EKA2) starting with version 8.0b. Some embedded systems use operating systems such as Palm OS, BSD, and Linux, although such operating systems do not support real-time computing. Operating system development as a hobby A hobby operating system may be classified as one whose code has not been directly derived from an existing operating system, and has few users and active developers. In some cases, hobby development is in support of a "homebrew" computing device, for example, a simple single-board computer powered by a 6502 microprocessor. Or, development may be for an architecture already in widespread use. Operating system development may come from entirely new concepts, or may commence by modeling an existing operating system. In either case, the hobbyist is his/her own developer, or may interact with a small and sometimes unstructured group of individuals who have like interests. Examples of a hobby operating system include Syllable and TempleOS. Diversity of operating systems and portability Application software is generally written for use on a specific operating system, and sometimes even for specific hardware. When porting the application to run on another OS, the functionality required by that application may be implemented differently by that OS (the names of functions, meaning of arguments, etc.) requiring the application to be adapted, changed, or otherwise maintained. Unix was the first operating system not written in assembly language, making it very portable to systems different from its native PDP-11. This cost in supporting operating systems diversity can be avoided by instead writing applications against software platforms such as Java or Qt. These abstractions have already borne the cost of adaptation to specific operating systems and their system libraries. Another approach is for operating system vendors to adopt standards. For example, POSIX and OS abstraction layers provide commonalities that reduce porting costs. Market share See also Comparison of operating systems Crash (computing) Hypervisor Interruptible operating system List of important publications in operating systems List of operating systems List of pioneers in computer science Live CD Glossary of operating systems terms Microcontroller Mobile device Mobile operating system Network operating system Object-oriented operating system Operating System Projects System Commander System image Timeline of operating systems Notes References Further reading O'Brien, J. A., & Marakas, G. M.(2011). Management Information Systems. 10e. McGraw-Hill Irwin. External links Multics History and the history of operating systems	Operating System (OS)	0
List of operating systems This is a list of operating systems. Computer operating systems can be categorized by technology, ownership, licensing, working state, usage, and by many other characteristics. In practice, many of these groupings may overlap. Criteria for inclusion is notability, as shown either through an existing Wikipedia article or citation to a reliable source. Proprietary Acorn Computers Arthur ARX MOS RISC iX RISC OS Amazon Fire OS Amiga Inc. AmigaOS AmigaOS 1.0-3.9 (Motorola 68000) AmigaOS 4 (PowerPC) Amiga Unix (a.k.a. Amix) Amstrad AMSDOS Contiki CP/M 2.2 CP/M Plus SymbOS Apple Inc. Apple II family Apple DOS Apple Pascal ProDOS GS/OS GNO/ME Contiki Apple III Apple SOS Apple Lisa Apple Macintosh Classic Mac OS A/UX (UNIX System V with BSD extensions) Copland MkLinux Pink Rhapsody macOS (formerly Mac OS X and OS X) macOS Server (formerly Mac OS X Server and OS X Server) Apple Network Server IBM AIX (Apple-customized) Apple MessagePad Newton OS iPhone and iPod Touch iOS (formerly iPhone OS) iPad iPadOS Apple Watch watchOS Apple TV tvOS Embedded operating systems A/ROSE bridgeOS iPod software (unnamed embedded OS for iPod) Unnamed NetBSD variant for Airport Extreme and Time Capsule Apollo Computer, Hewlett-Packard Domain/OS – One of the first network-based systems. Run on Apollo/Domain hardware. Later bought by Hewlett-Packard. Atari Atari DOS (for 8-bit computers) Atari TOS Atari MultiTOS Contiki (for 8-bit, ST, Portfolio) BAE Systems XTS-400 Be Inc. BeOS BeIA BeOS r5.1d0 magnussoft ZETA (based on BeOS r5.1d0 source code, developed by yellowTAB) Bell Labs Unix ("Ken's new system," for its creator (Ken Thompson), officially Unics and then Unix, the prototypic operating system created in Bell Labs in 1969 that formed the basis for the Unix family of operating systems) UNIX Time-Sharing System v1 UNIX Time-Sharing System v2 UNIX Time-Sharing System v3 UNIX Time-Sharing System v4 UNIX Time-Sharing System v5 UNIX Time-Sharing System v6 MINI-UNIX PWB/UNIX USG CB Unix UNIX Time-Sharing System v7 (It is from Version 7 Unix (and, to an extent, its descendants listed below) that almost all Unix-based and Unix-like operating systems descend.) Unix System III Unix System IV Unix System V Unix System V Releases 2.0, 3.0, 3.2, 4.0, and 4.2 UNIX Time-Sharing System v8 UNIX Time-Sharing System v9 UNIX Time-Sharing System v10 Non-Unix Operating Systems: BESYS Plan 9 from Bell Labs Inferno Burroughs Corporation, Unisys Burroughs MCP Commodore International GEOS AmigaOS AROS Research Operating System Control Data Corporation Lower 3000 series SCOPE (Supervisory Control Of Program Execution) Upper 3000 series SCOPE (Supervisory Control Of Program Execution) Drum SCOPE 6x00 and related Cyber Chippewa Operating System (COS) MACE (Mansfield and Cahlander Executive) Kronos (Kronographic OS) NOS (Network Operating System) NOS/VE NOS Virtual Environment SCOPE (Supervisory Control Of Program Execution) NOS/BE NOS Batch Environment SIPROS (Simultaneous Processing Operating System) CloudMosa Puffin OS Convergent Technologies Convergent Technologies Operating System – later acquired by Unisys Cromemco Cromemco DOS (CDOS) – a Disk Operating system compatible with CP/M Cromix – a multitasking, multi-user, Unix-like OS for Cromemco microcomputers with Z80A and/or 68000 CPU Data General AOS for 16-bit Data General Eclipse computers and AOS/VS for 32-bit (MV series) Eclipses, MP/AOS for microNOVA-based computers DG/UX RDOS Real-time Disk Operating System, with variants: RTOS and DOS (not related to PC DOS, MS-DOS etc.) Datapoint CTOS Cassette Tape Operating System for the Datapoint 2200 DOS Disk Operating System for the Datapoint 2200, 5500, and 1100 DDC-I, Inc. Deos – Time & Space Partitioned RTOS, Certified to DO-178B, Level A since 1998 HeartOS – POSIX-based Hard Real-Time Operating System Digital Research, Inc. CP/M CP/M CP/M for Intel 8080/8085 and Zilog Z80 Personal CP/M, a refinement of CP/M CP/M Plus with BDOS 3.0 CP/M-68K CP/M for Motorola 68000 CP/M-8000 CP/M for Zilog Z8000 CP/M-86 CP/M for Intel 8088/8086 CP/M-86 Plus Personal CP/M-86 MP/M Multi-user version of CP/M-80 MP/M II MP/M-86 Multi-user version of CP/M-86 MP/M 8-16, a dual-processor variant of MP/M for 8086 and 8080 CPUs. Concurrent CP/M, the successor of CP/M-80 and MP/M-80 Concurrent CP/M-86, the successor of CP/M-86 and MP/M-86 Concurrent CP/M 8-16, a dual-processor variant of Concurrent CP/M for 8086 and 8080 CPUs. Concurrent CP/M-68K, a variant for the 68000 DOS Concurrent DOS, the successor of Concurrent CP/M-86 with PC-MODE Concurrent PC DOS, a Concurrent DOS variant for IBM compatible PCs Concurrent DOS 8-16, a dual-processor variant of Concurrent DOS for 8086 and 8080 CPUs Concurrent DOS 286 Concurrent DOS XM, a real-mode variant of Concurrent DOS with EEMS support Concurrent DOS 386 Concurrent DOS 386/MGE, a Concurrent DOS 386 variant with advanced graphics terminal capabilities Concurrent DOS 68K, a port of Concurrent DOS to Motorola 68000 CPUs with DOS source code portability capabilities FlexOS 1.0 – 2.34, a derivative of Concurrent DOS 286 FlexOS 186, a variant of FlexOS for terminals FlexOS 286, a variant of FlexOS for hosts Siemens S5-DOS/MT, an industrial control system based on FlexOS IBM 4680 OS, a POS operating system based on FlexOS IBM 4690 OS, a POS operating system based on FlexOS Toshiba 4690 OS, a POS operating system based on IBM 4690 OS and FlexOS FlexOS 386, a later variant of FlexOS for hosts IBM 4690 OS, a POS operating system based on FlexOS Toshiba 4690 OS, a POS operating system based on IBM 4690 OS and FlexOS FlexOS 68K, a derivative of Concurrent DOS 68K Multiuser DOS, the successor of Concurrent DOS 386 CCI Multiuser DOS Datapac Multiuser DOS Datapac System Manager, a derivative of Datapac Multiuser DOS IMS Multiuser DOS IMS REAL/32, a derivative of Multiuser DOS IMS REAL/NG, the successor of REAL/32 DOS Plus 1.1 – 2.1, a single-user, multi-tasking system derived from Concurrent DOS 4.1 – 5.0 DR-DOS 3.31 – 6.0, a single-user, single-tasking native DOS derived from Concurrent DOS 6.0 Novell PalmDOS 1.0 Novell "Star Trek" Novell DOS 7, a single-user, multi-tasking system derived from DR DOS Caldera OpenDOS 7.01 Caldera DR-DOS 7.02 and higher Digital Equipment Corporation, Compaq, Hewlett-Packard, Hewlett Packard Enterprise Batch-11/DOS-11 OS/8 RSTS/E – multi-user time-sharing OS for PDP-11s RSX-11 – multiuser, multitasking OS for PDP-11s RT-11 – single user OS for PDP-11 TOPS-10 – for the PDP-10 TENEX – an ancestor of TOPS-20 from BBN, for the PDP-10 TOPS-20 – for the PDP-10 DEC MICA – for the DEC PRISM Digital UNIX – derived from OSF/1, became HP's Tru64 UNIX Ultrix VMS – originally by DEC and HP now by VMS Software Inc.) for the VAX mini-computer range, Alpha and Intel Itanium i2 and i4; later renamed OpenVMS WAITS – for the PDP-6 and PDP-10 ENEA AB OSE – Flexible, small footprint, high-performance RTOS for control processors Fujitsu Towns OS XSP OS/IV MSP MSP-EX General Electric, Honeywell, Bull Real-Time Multiprogramming Operating System GCOS Multics Google Chromium OS is an open source operating system development version of Chrome OS. Both operating systems are based on the Linux kernel. Chrome OS is designed to work exclusively with web applications. Announced on July 7, 2009, Chrome OS is currently publicly available and was released summer 2011. The Chrome OS source code was released on November 19, 2009, under the BSD license as Chromium OS. Container-Optimized OS (COS) is an operating system that is optimized for running Docker containers, based on Chromium OS. Android is an operating system for mobile devices. It consists of Android Runtime (userland) with Linux (kernel), with its Linux kernel modified to add drivers for mobile device hardware and to remove unused Vanilla Linux drivers. gLinux, a Linux distribution that Google uses internally Fuchsia is a capability-based, real-time, operating system (RTOS) scalable to universal devices, in early development, from the tiniest embedded hardware, wristwatches, tablets to the largest personal computers. Unlike Chrome OS and Android, it is not based on the Linux kernel, but instead began on a new microkernel called "Zircon", derived from "Little Kernel". Wear OS a version of Google's Android operating system designed for smartwatches and other wearables. Green Hills Software INTEGRITY – Reliable Operating system INTEGRITY-178B – A DO-178B certified version of INTEGRITY. µ-velOSity – A lightweight microkernel. Harris Corporation Vulcan O/S – Proprietary O/S for Harris' Computer Systems (HCX) Harris UNIX – Proprietary UNIX based OS for Harris' Computers (MCX) Heathkit, Zenith Data Systems HDOS – ran on the H8 and Heath/Zenith Z-89 series HT-11 – a modified version of RT-11 that ran on the Heathkit H11 Hewlett-Packard, Hewlett Packard Enterprise HP Multi-Programming Executive (MPE, MPE/XL, and MPE/iX) – runs on HP 3000 and HP e3000 mini-computers HP-UX – runs on HP9000 and Itanium servers (from small to mainframe-class computers) Honeywell CP-6 Huawei Harmony OS LiteOS Intel Corporation iRMX – real-time operating system originally created to support the Intel 8080 and 8086 processor families in embedded applications. ISIS, ISIS-II – "Intel Systems Implementation Supervisor" was an environment for development of software within the Intel microprocessor family in the early 1980s on their Intellec Microcomputer Development System and clones. ISIS-II worked with 8 inch floppy disks and had an editor, cross-assemblers, a linker, an object locator, debugger, compilers for PL/M, a BASIC interpreter, etc. and allowed file management through a console. IBM On early mainframes: 1410, 7010, 704, 709, 7090, 7094, 7040, 7044, 7030 BESYS – for the IBM 7090 Compatible Time-Sharing System (CTSS) – developed at MIT's Computation Center for use on a modified IBM 7094 FORTRAN Monitor System (FMS) – for the IBM 709 and 7090 GM OS & GM-NAA I/O – for the IBM 704 IBSYS – tape based operating system for IBM 7090 and IBM 7094 7040/7044 Operating System (16/32K) - 7040-PR-150 IJMON – A bootable serial I/O monitor for loading programs for the IBM 1400 series 1410 Processor Operating System (PR-155) for the 1410 and 7010 SHARE Operating System (SOS) – for the IBM 704 and 709 University of Michigan Executive System (UMES) – for the IBM 704, 709, and 7090) On S/360, S/370, and successor mainframes OS/360 and successors on IBM S/360, S/370, and successor mainframes OS/360 (first official OS targeted for the System/360 architecture) PCP (Primary Control Program, a kernel and a ground breaking automatic space allocating file system) MFT (original Multi-programming with a Fixed number of Tasks, replaced by MFT II) MFT II (Multi-Programming with a Fixed number of Tasks, had up to 15 fixed size application partitions, plus partitions for system tasks, initially defined at boot time but redefinable by operator command) MVT (Multi-Programming with a Variable number of Tasks, had up to 15 application regions defined dynamically, plus additional regions for system tasks) M65MP (MVT with support for a multiprocessor 360/65) OS/VS (port of OS/360 targeted for the System/370 virtual memory architecture (OS/370 is not the correct name for OS/VS1 and OS/VS2.) OS/VS has the following variations: OS/VS1 (Operating System/Virtual Storage 1, Virtual-memory version of OS/360 MFT II) OS/VS1 Basic Programming Extensions (BPE) adds device support and VM handshaking OS/VS2 (Operating System/Virtual Storage 2, Virtual-memory version of OS/360 MVT) OS/VS2 R1 (Called Single Virtual Storage (SVS), Virtual-memory version of OS/360 MVT but without multiprocessing support) OS/VS2 R2 through R3.8 (called Multiple Virtual Storage, MVS, eliminated most need for VS1). MVS/SE (MVS System Extensions) MVS/SP (MVS System Product) V1 MVS/370 refers to OS/VS2 MVS, MVS/SE and MVS/SP Version 1 MVS/XA (MVS/SP V2, supports S/370 Extended Architecture, 31-bit addressing) MVS/ESA (MVS supported Enterprise Systems Architecture, horizontal addressing extensions: data only address spaces called Dataspaces) MVS/SP V3 MVS/ESA SP V4 (a Unix environment was available for MVS/ESA SP V4R3) MVS/ESA SP V5 (the UNIX environment was bundled in this and all subsequent versions) OS/390 replacement for MVS/ESA SP V5 with some products bundled z/OS z/Architecture replacement for OS/390 with 64-bit virtual addressing Phoenix/MVS (Developed at Cambridge University) DOS/360 and successors on IBM S/360, S/370, and successor mainframes BOS/360 (early interim version of DOS/360, briefly available at a few Alpha & Beta System/360 sites) TOS/360 (similar to BOS above and more fleeting, able to boot and run from 2x00 series tape drives) DOS/360 (Disk Operating System (DOS), multi-programming system with up to 3 partitions, first commonly available OS for System/360) DOS/360/RJE (DOS/360 with a control program extension that provided for the monitoring of remote job entry hardware (card reader & printer) connected by dedicated phone lines) DOS/VS (First DOS offered on System/370 systems, provided virtual storage) DOS/VSE (also known as VSE, upgrade of DOS/VS, up to 14 fixed size processing partitions ) VSE/Advanced Functions (VSE/AF) - Additional functionality for DOS/VSE VSE/SP (program product including DOS/VSE and VSE/AF) VSE/ESA, replaces VSE/SP, supports ESA/370 and ESA/390 with 31-bit addresses z/VSE (latest version of the four decades old DOS lineage, supports 64-bit addresses, multiprocessing, multiprogramming, SNA, TCP/IP, and some virtual machine features in support of Linux workloads) CP/CMS (Control Program/Cambridge Monitor System) and successors on IBM S/360, S/370, and successor mainframes CP-40/CMS (for System/360 Model 40) CP-67/CMS (for System/360 Model 67) Virtual Machine Facility/370 (VM/370) - the CP virtual machine hypervisor, Conversational Monitor System (CMS) operating system and supporting facilities for System/370 (24-bit addresses) VM/370 Basic System Extensions Program Product (VM/BSE, AKA BSEPP) is an enhancement to VM/370 VM/370 System Extensions Program Product (VM/SE, AKA SEPP) is an enhancement to VM/370 that includes the facilities of VM/BSE Virtual Machine/System Product (VM/SP) replaces VM/370, VM/BSE and VM/SE. Virtual Machine/Extended Architecture (VM/XA) refers to three versions of VM that support System/370 Extended Architecture (S/370-XA) with 31-bit virtual addresses Virtual Machine/Extended architecture Migration Aid (VM/XA MA) - Intended for MVS/370 to MVS/XA migration Virtual Machine/Extended Architecture Systems Facility (VM/XA SF) - new release of VM/XA MA with additional functionality Virtual Machine/Extended Architecture System Product (VM/XA SP) - Replaces VM/SP, VM/SP HPO and VM/XA SF VM/ESA (Virtual Machine/Enterprise Systems Architecture, supports S/370, ESA/370 and ESA/390) z/VM (z/Architecture version of the VM OS with 64-bit addressing) TPF Line (Transaction Processing Facility) on IBM S/360, S/370, and successor mainframes (largely used by airlines) ACP (Airline Control Program) TPF (Transaction Processing Facility) z/TPF (z/Architecture extension) Unix-like on IBM S/360, S/370, and successor mainframes AIX/370 (IBM's Advanced Interactive eXecutive, a System V Unix version) AIX/ESA (IBM's Advanced Interactive eXecutive, a System V Unix version) OpenSolaris for System z UTS (developed by Amdahl) Linux on IBM Z Others on IBM S/360, S/370, and successor mainframes: BOS/360 (Basic Operating System) Distributed Processing Programming Executive/370 (DPPX/370) a port of DDPX from 8100 to S/370. MTS (Michigan Terminal System, developed by a group of universities in the US, Canada, and the UK for the IBM System/360 Model 67, System/370 series, and compatible mainframes) RTOS/360 (IBM's Real Time Operating System, ran on 5 NASA custom System/360-75s) TOS/360 (Tape Operating System) TSS/360 (IBM's Time Sharing System) MUSIC/SP (developed by McGill University for IBM System/370) ORVYL and WYLBUR (developed by Stanford University for IBM System/360) On PC and Intel x86 based architectures PC DOS, IBM DOS PC DOS 1.x, 2.x, 3.x (developed jointly with Microsoft) IBM DOS 4.x, 5.0 (developed jointly with Microsoft) PC DOS 6.1, 6.3, 7, 2000, 7.10 OS/2 OS/2 1.x (developed jointly with Microsoft) OS/2 2.x OS/2 Warp 3 (ported to PPC via Workplace OS) OS/2 Warp 4 eComStation (Warp 4.5/Workspace on Demand, rebundled by Serenity Systems International) ArcaOS (Warp 4.52 based system sold by Arca Noae, LLC) IBM 4680 OS version 1 to 4, a POS operating system based on Digital Research's Concurrent DOS 286 and FlexOS 286 1.xx IBM 4690 OS version 1 to 6.3, a successor to 4680 OS based on Novell's FlexOS 286/FlexOS 386 2.3x Toshiba 4690 OS version 6.4, a successor to 4690 OS 6.3 Unix-like on PS/2 AIX (IBM's Advanced Interactive eXecutive, a System V Unix version) On other hardware platforms IBM Series/1 EDX (Event Driven Executive) RPS (Realtime Programming System) CPS (Control Programming Support, subset of RPS) SerIX (Unix on Series/1) IBM 1130 DMS (Disk Monitor System) IBM 1800 TSX (Time Sharing eXecutive) MPX (Multi Programming eXecutive) IBM 8100 DPCX (Distributed Processing Control eXecutive) DPPX (Distributed Processing Programming Executive) IBM System/3 DMS (Disk Management System) IBM System/34, IBM System/36 SSP (System Support Program) IBM System/38 CPF (Control Program Facility) IBM System/88 Stratus VOS (developed by Stratus, and used for IBM System/88, Original equipment manufacturer from Stratus) IBM AS/400, iSeries, System i, IBM Power Systems IBM i (previously known as OS/400 and i5/OS, descendant of System/38 CPF, includes System/36 SSP and AIX environment) UNIX on IBM RT PC AOS (a BSD Unix version, not related to Data General AOS) AIX (Advanced Interactive eXecutive, a System V Unix version) UNIX on POWER ISA, PowerPC, and Power ISA AIX (Advanced Interactive eXecutive, a System V Unix version) Others Workplace OS (a microkernel based operating system including OS/2, developed and canceled in the 1990s) K42 (open-source research operating system on PowerPC or x86 based cache-coherent multiprocessor systems) Dynix (developed by Sequent, and used for IBM NUMA-Q too) International Computers Limited J and MultiJob – for the System 4 series mainframes GEORGE 2/3/4 GEneral ORGanisational Environment – used by ICL 1900 series mainframes Executive – used on the 1900 and 290x range of minicomputers. A modified version of Executive was also used as part of GEORGE 3 and 4. TME – used on the ME29 minicomputer ICL VME – including early variants VME/B and VME/2900, appearing on the ICL 2900 Series and Series 39 mainframes, implemented in S3 VME/K – on early smaller 2900s Jide Remix OS Jolla Sailfish OS KaiOS KaiOS Lynx Real-time Systems, LynuxWorks, Lynx Software Technologies LynxOS Meizu Flyme OS Micrium Inc. MicroC/OS-II – a small pre-emptive priority based multi-tasking kernel MicroC/OS-III – a small pre-emptive priority based multi-tasking kernel, with unlimited number of tasks and priorities, and round-robin scheduling Microsoft Corporation Xenix (licensed version of Unix; licensed to SCO in 1987) MS-DOS (developed jointly with IBM, versions 1.0–6.22) MSX-DOS (developed by MS Japan for the MSX 8-bit computer) DOS/V OS/2 1.x (developed jointly with IBM until version 1.3) Windows (16-bit and 32-bit preemptive and cooperative multitasking, running atop MS-DOS) Windows 1.0 (Windows 1) Windows 2.0 (Windows 2 – separate version for i386 processor) Windows 3.0 (Windows 3) Windows 3.1x (Windows 3.1) Windows for Workgroups 3.1 (Codename Snowball) Windows 3.2 (Chinese-only release) Windows for Workgroups 3.11 Windows 95 (codename Chicago – Windows 4.0) Windows 98 (codename Memphis – Windows 4.1) Windows Millennium Edition (Windows ME – Windows 4.9) Windows NT (Full 32-bit or 64-bit kernel, not dependent on MS-DOS) Windows NT 3.1 Windows NT 3.5 Windows NT 3.51 Windows NT 4.0 Windows 2000 (Windows NT 5.0) Windows XP (Windows NT 5.1) Windows Server 2003 (Windows NT 5.2) Windows Fundamentals for Legacy PCs (based on Windows XP) Windows Vista (Windows NT 6.0) Windows Azure (Cloud OS Platform) 2009 Windows Home Server (based on Windows Server 2003) Windows Server 2008 (based on Windows Vista) Windows 7 (Windows NT 6.1) Windows Phone 7 Windows Server 2008 R2 (based on Windows 7) Windows Home Server 2011 (based on Windows Server 2008 R2) Windows 8 (Windows NT 6.2) Windows RT Windows Phone 8 Windows Server 2012 (based on Windows 8) Windows 8.1 (Windows NT 6.3) Windows Phone 8.1 Windows Server 2012 R2 (based on Windows 8.1) Windows 10 (Windows NT 10) Windows 10 Mobile Windows Server 2016 Windows Server 2019 Windows 11 Windows CE (OS for handhelds, embedded devices, and real-time applications that is similar to other versions of Windows) Windows CE 3.0 Windows CE 5.0 Windows Embedded CE 6.0 Windows Embedded Compact 7 Windows Embedded Compact 2013 Windows Mobile (based on Windows CE, but for a smaller form factor) Singularity – A research operating system written mostly in managed code (C#) Midori – A managed code operating system Xbox system software Xbox 360 system software Xbox One system software Azure Sphere ThreadX MITS Altair DOS – An early disk operating system for the Altair 8800 machine. MontaVista MontaVista Mobilinux NCR Corporation TMX – Transaction Management eXecutive IMOS – Interactive Multiprogramming Operating System (circa 1978), for the NCR Century 8200 series minicomputers VRX – Virtual Resource eXecutive Nintendo ES is a computer operating system developed originally by Nintendo and since 2008 by Esrille. It is open source and runs natively on x86 platforms. NeXT NeXTSTEP Novell NetWare – network operating system providing high-performance network services. Has been superseded by Open Enterprise Server line, which can be based on NetWare or Linux to provide the same set of services. UnixWare Novell "SuperNOS" – a never released merge of NetWare and UnixWare Novell "Corsair" Novell "Exposé" Open Enterprise Server – the successor to NetWare Open Mobile Platform Aurora OS – the successor to Sailfish OS (not to be confused with a different Aurora OS) Quadros Systems RTXC Quadros RTOS – proprietary C-based RTOS used in embedded systems RCA Time Sharing Operating System (TSOS) – first OS supporting virtual addressing of the main storage and support for both timeshare and batch interface RoweBots DSPnano RTOS – 8/16 Bit Ultra Tiny Embedded Linux Compatible RTOS Samsung Electronics Bada Tizen is an operating system based on the Linux kernel, a project within the Linux Foundation and is governed by a Technical Steering Group (TSG) while controlled by Samsung and backed by Intel. Tizen works on a wide range of Samsung devices including smartphones, tablets, smart TVs, PCs and wearable. Orsay One UI - Android skin Sinclair Research Sinclair BASIC was used in the 8-bit home computers from Sinclair Research and Timex Sinclair. It was included in the ROM, and the computers booted to the Basic interpreter. Various versions exist, with the latter ones supporting disk drive operations. SCO, SCO Group Xenix, Unix System III based distribution for the Intel 8086/8088 architecture Xenix 286, Unix System V Release 2 based distribution for the Intel 80286 architecture Xenix 386, Unix System V Release 2 based distribution for the Intel 80386 architecture SCO Unix, SCO UNIX System V/386 was the first volume commercial product licensed by AT&T to use the UNIX System trademark (1989). Derived from AT&T System V Release 3.2 with an infusion of Xenix device drivers and utilities plus most of the SVR4 features SCO Open Desktop, the first 32-bit graphical user interface for UNIX Systems running on Intel processor-based computers. Based on SCO Unix SCO OpenServer 5, AT&T UNIX System V Release 3 based SCO OpenServer 6, SVR5 (UnixWare 7) based kernel with SCO OpenServer 5 application and binary compatibility, system administration, and user environments UnixWare UnixWare 2.x, based on AT&T System V Release 4.2MP UnixWare 7, UnixWare 2 kernel plus parts of 3.2v5 (UnixWare 2 + OpenServer 5 = UnixWare 7). Referred to by SCO as SVR5 Scientific Data Systems (SDS) Berkeley Timesharing System for the SDS 940 SYSGO PikeOS – a certified real time operating system for safety and security critical embedded systems Tandem Computers, Compaq, Hewlett-Packard, Hewlett Packard Enterprise NonStop OS – runs on HP's NonStop line of Itanium servers Tandy Corporation TRSDOS – A floppy-disk-oriented OS supplied by Tandy/Radio Shack for their TRS-80 Z80-based line of personal computers. Eventually renamed as LS-DOS or LDOS. Color BASIC – A ROM-based OS created by Microsoft for the TRS-80 Color Computer. NewDos/80 – A third-party OS for Tandy's TRS-80 personal computers. DeskMate – Operating system created by Tandy Corporation and introduced with the Tandy 1000 computer. TCSC (later NCSC) Edos – enhanced version of IBM's DOS/360 (and later DOS/VS and DOS/VSE) operating system for System/360 and System/370 IBM mainframes Texas Instruments TI-RTOS Kernel – Real-time operating system for TI's embedded devices. TRON Project TRON – open real-time operating system kernel T-Kernel UNIVAC, Unisys EXEC I EXEC II EXEC 8/OS 1100/OS 2200 VS/9, successor to RCA TSOS Wang Laboratories WPS Wang Word Processing System. Micro-code based system. OIS Wang Office Information System. Successor to the WPS. Combined the WPS and VP/MVP systems. Wind River Systems VxWorks – Small footprint, scalable, high-performance RTOS for embedded microprocessor based systems. Zilog Z80-RIO Other Lisp-based Lisp Machines, Inc. (also known as LMI) used an operating system written in MIT's Lisp Machine Lisp. Symbolics Genera written in a systems dialect of the Lisp programming language called ZetaLisp and Symbolics Common Lisp. Genera was ported to a virtual machine for the DEC Alpha line of computers. Texas Instruments' Explorer Lisp machine workstations also had systems code written in Lisp Machine Lisp. Xerox 1100 series of Lisp machines used an operating system also written in Interlisp, and was also ported to a virtual machine called "Medley." For Elektronika BK ANDOS CSI-DOS MK-DOS Non-standard language-based Pilot operating system – written in the Mesa language and used on Xerox Star workstations. PERQ Operating System (POS) – written in PERQ Pascal. Other proprietary non-Unix-like Эльбрус-1 (Elbrus-1) and Эльбрус-2 – used for application, job control, system programming, implemented in uЭль-76 (AL-76). EOS – developed by ETA Systems for use in their ETA-10 line of supercomputers EMBOS – developed by Elxsi for use on their mini-supercomputers GCOS – a proprietary Operating System originally developed by General Electric MAI Basic Four – An OS implementing Business Basic from MAI Systems. Michigan Terminal System – Developed by a group of universities in the US, Canada, and the UK for use on the IBM System/360 Model 67, the System/370 series, and compatible mainframes MUSIC/SP – an operating system developed for the S/370, running normally under VM OS ES – an operating system for ES EVM PC-MOS/386 – DOS-like, but multiuser/multitasking Prolog-Dispatcher – used to control Soviet Buran space shuttle. SINTRAN III – an operating system used with Norsk Data computers. SkyOS – commercial desktop OS for PCs SODA – used by the Odra 1204 computers. THEOS TSX-32 – a 32-bit operating system for x86 platform. TX990/TXDS, DX10 and DNOS – proprietary operating systems for TI-990 minicomputers Other proprietary Unix-like and POSIX-compliant Aegis (Apollo Computer) Amiga Unix (Amiga ports of Unix System V release 3.2 with Amiga A2500UX and SVR4 with Amiga A3000UX. Started in 1990, last version was in 1992) Coherent (Unix-like OS from Mark Williams Co. for PC class computers) DC/OSx (DataCenter/OSx—an operating system developed by Pyramid Technology for its MIPS-based systems) DG/UX (Data General Corp) DNIX from DIAB DSPnano RTOS (POSIX nanokernel, DSP Optimized, Open Source) HeliOS developed and sold by Perihelion Software mainly for transputer-based systems Interactive Unix (a port of the UNIX System V operating system for Intel x86 by Interactive Systems Corporation) IRIX from SGI MeikOS NeXTSTEP (developed by NeXT; a Unix-based OS based on the Mach microkernel) OS-9 Unix-like RTOS. (OS from Microware for Motorola 6809 based microcomputers) OS9/68K Unix-like RTOS. (OS from Microware for Motorola 680x0 based microcomputers; based on OS-9) OS-9000 Unix-like RTOS. (OS from Microware for Intel x86 based microcomputers; based on OS-9, written in C) OSF/1 (developed into a commercial offering by Digital Equipment Corporation) OPENSTEP QNX (POSIX, microkernel OS; usually a real time embedded OS) Rhapsody (an early form of Mac OS X) RISC iX – derived from BSD 4.3, by Acorn computers, for their ARM family of machines RISC/os (a port by MIPS Technologies of 4.3BSD for its MIPS-based computers) RMX SCO UNIX (from SCO, bought by Caldera who renamed themselves SCO Group) SINIX (a port by SNI of Unix to the MIPS architecture) Solaris (from Sun, bought by Oracle; a System V-based replacement for SunOS) SunOS (BSD-based Unix system used on early Sun hardware) SUPER-UX (a port of System V Release 4.2MP with features adopted from BSD and Linux for NEC SX architecture supercomputers) System V (a release of AT&T Unix, 'SVR4' was the 4th minor release) System V/AT, 386 (The first version of AT&T System V UNIX on the IBM 286 and 386 PCs, ported and sold by Microport) Trusted Solaris (Solaris with kernel and other enhancements to support multilevel security) UniFLEX (Unix-like OS from TSC for DMA-capable, extended addresses, Motorola 6809 based computers; e.g. SWTPC, GIMIX and others) Unicos (the version of Unix designed for Cray Supercomputers, mainly geared to vector calculations) UTX-32 (Developed by Gould CSD (Computer System Division), a Unix-based OS that included both BSD and System V characteristics. It was one of the first Unix based systems to receive NSA's C2 security level certification.) Zenix, Zenith corporations Unix (a popular USA electronics maker at the time) Non-proprietary Unix or Unix-like MINIX (study OS developed by Andrew S. Tanenbaum in the Netherlands) BSD (Berkeley Software Distribution, a variant of Unix for DEC VAX hardware) FreeBSD (one of the outgrowths of UC Regents' abandonment of CSRG's 'BSD Unix') DragonFlyBSD, forked from FreeBSD 4.8 MidnightBSD, forked from FreeBSD 6.1 GhostBSD TrueOS (previously known as PC-BSD) NetBSD (an embedded device BSD variant) OpenBSD forked from NetBSD Bitrig forked from OpenBSD Darwin, created by Apple using code from NeXTSTEP, FreeBSD, and NetBSD GNU (also known as GNU/Hurd) Linux (see also List of Linux distributions) (alleged to be GNU/Linux see GNU/Linux naming controversy) Android Android-x86 Remix OS Redox (written in Rust) OpenSolaris illumos, contains original Unix (SVR4) code derived from the OpenSolaris (discontinued by Oracle in favor of Solaris 11 Express) OpenIndiana, operates under the illumos Foundation. Uses the illumos kernel, which is a derivative of OS/Net, which is basically an OpenSolaris/Solaris kernel with the bulk of the drivers, core libraries, and basic utilities. Nexenta OS, based on the illumos kernel with Ubuntu packages SmartOS, an illumos distribution for cloud computing with Kernel-based Virtual Machine integration. RTEMS (Real-Time Executive for Multiprocessor Systems) Syllable Desktop VSTa Plurix (or Tropix) (by Federal University of Rio de Janeiro – UFRJ) TUNIS (University of Toronto) Xv6 - a simple Unix-like teaching operating system from MIT SerenityOS - aims to be a modern Unix-like operating system, yet with a look and feel that emulates 1990s operating systems such as Microsoft Windows and Mac OS. Non-Unix Cosmos – written in C# FreeDOS – open source DOS variant Genode – operating system framework for microkernels (written in C++) Ghost OS – written in assembly, C/C++ Haiku – open source inspired by BeOS, in development Incompatible Timesharing System (ITS) – written in the MIDAS macro assembler language for the PDP-6 and PDP-10 by MIT students osFree – OS/2 Warp open source clone OSv – written in C++ Phantom OS – persistent object-oriented ReactOS – open source OS designed to be binary compatible with Windows NT and its variants (Windows XP, Windows 2000, etc.); in development SharpOS – written in .NET C# TempleOS – written in HolyC Visopsys – written in C and assembly by Andy McLaughlin Research Unix or Unix-like Plan 9 from Bell Labs – distributed OS developed at Bell Labs, based on original Unix design principles yet functionally different and going much further Inferno – distributed OS derived from Plan 9, originally from Bell Labs Research Unix Non-Unix Amoeba – research OS by Andrew S. Tanenbaum Barrelfish Croquet EROS – microkernel, capability-based CapROS – microkernel EROS successor Harmony – realtime, multitasking, multiprocessing message-passing system developed at the National Research Council of Canada. HelenOS – research and experimental operating system House – Haskell User's Operating System and Environment, research OS written in Haskell and C ILIOS – Research OS designed for routing L4 – second generation microkernel Mach – from OS kernel research at Carnegie Mellon University; see NeXTSTEP Nemesis – Cambridge University research OS – detailed quality of service abilities Singularity – experimental OS from Microsoft Research written in managed code to be highly dependable Spring – research OS from Sun Microsystems THE multiprogramming system – by Dijkstra in 1968, at the Eindhoven University of Technology in the Netherlands, introduced the first form of software-based memory segmentation, freeing programmers from being forced to use actual physical locations Thoth – realtime, multiprocess message-passing system developed at the University of Waterloo. V – from Stanford, early 1980s Verve – OS designed by Microsoft Research to be verified end-to-end for type safety and memory safety Xinu – Study OS developed by Douglas E. Comer in the United States Disk operating systems (DOS) 86-DOS (developed at Seattle Computer Products by Tim Paterson for the new Intel 808x CPUs; licensed to Microsoft, became PC DOS/MS-DOS. Also known by its working title QDOS.) PC DOS (IBM's DOS variant, developed jointly with Microsoft, versions 1.0–7.0, 2000, 7.10) MS-DOS (Microsoft's DOS variant for OEM, developed jointly with IBM, versions 1.x–6.22 Microsoft's now abandoned DOS variant) Concurrent CP/M-86 3.1 (BDOS 3.1) with PC-MODE (Digital Research's successor of CP/M-86 and MP/M-86) Concurrent DOS 3.1-4.1 (BDOS 3.1-4.1) Concurrent PC DOS 3.2 (BDOS 3.2) (Concurrent DOS variant for IBM compatible PCs) DOS Plus 1.1, 1.2 (BDOS 4.1), 2.1 (BDOS 5.0) (single-user, multi-tasking system derived from Concurrent DOS 4.1-5.0) Concurrent DOS 8-16 (dual-processor variant of Concurrent DOS for 8086 and 8080 CPUs) Concurrent DOS 286 1.x FlexOS 1.00-2.34 (derivative of Concurrent DOS 286) FlexOS 186 (variant of FlexOS for terminals) FlexOS 286 (variant of FlexOS for hosts) Siemens S5-DOS/MT (industrial control system based on FlexOS) IBM 4680 OS (POS operating system based on FlexOS) IBM 4690 OS (POS operating system based on FlexOS) Toshiba 4690 OS (POS operating system based on IBM 4690 OS and FlexOS) FlexOS 386 (later variant of FlexOS for hosts) IBM 4690 OS (POS operating system based on FlexOS) Toshiba 4690 OS (POS operating system based on IBM 4690 OS and FlexOS) Concurrent DOS 386 1.0, 1.1, 2.0, 3.0 (BDOS 5.0-6.2) Concurrent DOS 386/MGE (Concurrent DOS 386 variant with advanced graphics terminal capabilities) Multiuser DOS 5.0, 5.01, 5.1 (BDOS 6.3-6.6) (successor of Concurrent DOS 386) CCI Multiuser DOS 5.0-7.22 (up to BDOS 6.6) Datapac Multiuser DOS Datapac System Manager 7 (derivative of Datapac Multiuser DOS) IMS Multiuser DOS 5.1, 7.0, 7.1 (BDOS 6.6-6.7) IMS REAL/32 7.50, 7.51, 7.52, 7.53, 7.54, 7.60, 7.61, 7.62, 7.63, 7.70, 7.71, 7.72, 7.73, 7.74, 7.80, 7.81, 7.82, 7.83, 7.90, 7.91, 7.92, 7.93, 7.94, 7.95 (BDOS 6.8 and higher) (derivative of Multiuser DOS) IMS REAL/NG (successor of REAL/32) Concurrent DOS XM 5.0, 5.2, 6.0, 6.2 (BDOS 5.0-6.2) (real-mode variant of Concurrent DOS with EEMS support) DR DOS 3.31, 3.32, 3.33, 3.34, 3.35, 5.0, 6.0 (BDOS 6.0-7.1) single-user, single-tasking native DOS derived from Concurrent DOS 6.0) Novell PalmDOS 1 (BDOS 7.0) Novell DR DOS "StarTrek" Novell DOS 7 (single-user, multi-tasking system derived from DR DOS, BDOS 7.2) Novell DOS 7 updates 1-10 (BDOS 7.2) Caldera OpenDOS 7.01 (BDOS 7.2) Enhanced DR-DOS 7.01.0x (BDOS 7.2) Dell Real Mode Kernel (DRMK) Novell DOS 7 updates 11-15.2 (BDOS 7.2) Caldera DR-DOS 7.02-7.03 (BDOS 7.3) DR-DOS "WinBolt" OEM DR-DOS 7.04-7.05 (BDOS 7.3) OEM DR-DOS 7.06 (PQDOS) OEM DR-DOS 7.07 (BDOS 7.4/7.7) FreeDOS (open source DOS variant) ProDOS (operating system for the Apple II series computers) PTS-DOS (DOS variant by Russian company Phystechsoft) TurboDOS (Software 2000, Inc.) for Z80 and Intel 8086 processor-based systems Multi-tasking user interfaces and environments for DOS DESQview + QEMM 386 multi-tasking user interface for DOS DESQView/X (X-windowing GUI for DOS) Network operating systems Banyan VINES – by Banyan Systems Cambridge Ring Cisco IOS – by Cisco Systems Cisco NX-OS – previously SAN-OS CTOS – by Convergent Technologies, later acquired by Unisys Data ONTAP – by NetApp ExtremeWare – by Extreme Networks ExtremeXOS – by Extreme Networks Fabric OS – by Brocade JunOS – by Juniper NetWare – networking OS by Novell Network operating system (NOS) – developed by CDC for use in their Cyber line of supercomputers Novell Open Enterprise Server – Open Source networking OS by Novell. Can incorporate either SUSE Linux or Novell NetWare as its kernel Plan 9 – distributed OS developed at Bell Labs, based on Unix design principles but not functionally identical Inferno – distributed OS derived from Plan 9, originally from Bell Labs SONiC TurboDOS – by Software 2000, Inc. Generic, commodity, and other BLIS/COBOL A2 formerly named Active Object System (AOS), and then Bluebottle (a concurrent and active object update to the Oberon operating system) BS1000 by Siemens AG BS2000 by Siemens AG, now BS2000/OSD from Fujitsu-Siemens Computers (formerly Siemens Nixdorf Informationssysteme) BS3000 by Siemens AG (functionally similar to OS-IV and MSP from Fujitsu) Contiki for various, mostly 8-bit systems, including the Apple II series, the Atari 8-bit family, and some Commodore machines. FLEX9 (by Technical Systems Consultants (TSC) for Motorola 6809 based machines; successor to FLEX, which was for Motorola 6800 CPUs) Graphics Environment Manager (GEM) (windowing GUI for CP/M, DOS, and Atari TOS) GEOS (popular windowing GUI for PC, Commodore, Apple computers) JavaOS JNode (Java New Operating System Design Effort), written 99% in Java (native compiled), provides own JVM and JIT compiler. Based on GNU Classpath. JX Java operating system that focuses on a flexible and robust operating system architecture developed as an open source system by the University of Erlangen. KERNAL (default OS on Commodore 64) MERLIN for the Corvus Concept MorphOS (Amiga compatible) MSP by Fujitsu (successor to OS-IV), now MSP/EX, also known as Extended System Architecture (EXA), for 31-bit mode NetWare (networking OS by Novell) Oberon (operating system) (developed at ETH-Zürich by Niklaus Wirth et al.) for the Ceres and Chameleon workstation projects OSD/XC by Fujitsu-Siemens (BS2000 ported to an emulation on a Sun SPARC platform) OS-IV by Fujitsu (based on early versions of IBM's MVS) Pick (often licensed and renamed) PRIMOS by Prime Computer (sometimes spelled PR1MOS and PR1ME) Sinclair QDOS (multitasking for the Sinclair QL computer) SSB-DOS (by Technical Systems Consultants (TSC) for Smoke Signal Broadcasting; a variant of FLEX in most respects) SymbOS (GUI based multitasking operating system for Z80 computers) Symobi (GUI based modern micro-kernel OS for x86, ARM and PowerPC processors, developed by Miray Software; used and developed further at Technical University of Munich) TripOS, 1978 TurboDOS (Software 2000, Inc.) UCSD p-System (portable complete programming environment/operating system/virtual machine developed by a long running student project at UCSD; directed by Prof Kenneth Bowles; written in Pascal) VOS by Stratus Technologies with strong influence from Multics VOS3 by Hitachi for its IBM-compatible mainframes, based on IBM's MVS VM2000 by Siemens AG Visi On (first GUI for early PC machines; not commercially successful) VPS/VM (IBM based, main operating system at Boston University for over 10 years.) Hobby AROS – AROS Research Operating System (formerly known as Amiga Research Operating System) AtheOS – branched to become Syllable Desktop Syllable Desktop – a modern, independently originated OS; see AtheOS BareMetal DSPnano RTOS EmuTOS EROS – Extremely Reliable Operating System HelenOS – based on a preemptible microkernel design LSE/OS MenuetOS – extremely compact OS with GUI, written entirely in FASM assembly language KolibriOS – a fork of MenuetOS SerenityOS ToaruOS PonyOS Embedded Mobile operating systems DIP DOS on Atari Portfolio Embedded Linux (see also Linux for mobile devices) Android Flyme OS Replicant LineageOS See also List of custom Android distributions Firefox OS Ångström distribution Familiar Linux Mæmo based on Debian deployed on Nokia's Nokia 770, N800 and N810 Internet Tablets. OpenZaurus webOS from Palm, Inc., later Hewlett-Packard via acquisition, and most recently at LG Electronics through acquisition from Hewlett-Packard Access Linux Platform bada Openmoko Linux OPhone MeeGo (from merger of Maemo & Moblin) Mobilinux MotoMagx Qt Extended Sailfish OS Tizen (earlier called LiMo Platform) Ubuntu Touch PostmarketOS Inferno (distributed OS originally from Bell Labs) Magic Cap MS-DOS on Poqet PC, HP 95LX, HP 100LX, HP 200LX, HP 1000CX, HP OmniGo 700LX NetBSD Newton OS on Apple MessagePad Palm OS from Palm, Inc; now spun off as PalmSource PEN/GEOS on HP OmniGo 100 and 120 PenPoint OS Plan 9 from Bell Labs PVOS Symbian OS EPOC Windows CE, from Microsoft Pocket PC from Microsoft, a variant of Windows CE Windows Mobile from Microsoft, a variant of Windows CE Windows Phone from Microsoft DSPnano RTOS iOS watchOS tvOS iPod software iPodLinux iriver clix OS RockBox BlackBerry OS PEN/GEOS, GEOS-SC, GEOS-SE Palm OS Symbian platform (successor to Symbian OS) BlackBerry 10 Routers CatOS – by Cisco Systems Cisco IOS – originally Internetwork Operating System by Cisco Systems Inferno – distributed OS originally from Bell Labs IOS-XR – by Cisco Systems JunOS – by Juniper Networks LCOS – by LANCOM Systems Linux OpenWrt DD-WRT LEDE Gargoyle LibreCMC Zeroshell RTOS – by Force10 Networks FreeBSD m0n0wall OPNsense pfsense List of wireless router firmware projects Other embedded Apache Mynewt ChibiOS/RT Contiki ERIKA Enterprise eCos NetBSD Nucleus RTOS NuttX Minix NCOS freeRTOS, openRTOS, safeRTOS OpenEmbedded (or Yocto Project) pSOS (Portable Software On Silicon) QNX – Unix-like real-time operating system, aimed primarily at the embedded systems market. REX OS – microkernel; usually an embedded cell phone OS RIOT ROM-DOS TinyOS ThreadX RT-Thread DSPnano RTOS Windows IoT – formerly Windows Embedded Windows CE Windows IoT Core Windows IoT Enterprise Wind River VxWorks RTOS. Wombat – microkernel; usually real-time embedded Zephyr LEGO Mindstorms brickOS leJOS Capability-based Cambridge CAP computer – operating system demonstrated the use of security capabilities, both in hardware and software, also a useful fileserver, implemented in ALGOL 68C Flex machine – Custom microprogrammable hardware, with an operating system, (modular) compiler, editor, * garbage collector and filing system all written in ALGOL 68. HYDRA – Running on the C.mmp computer at Carnegie Mellon University, implemented in the programming language BLISS KeyKOS nanokernel EROS microkernel CapROS EROS successor V – from Stanford, early 1980s See also Comparison of operating systems Comparison of real-time operating systems Timeline of operating systems Category links Operating systems Embedded operating systems Real-time operating systems References External links "List of Operating Systems". www.operating-system.org. List of operating systems Computing-related lists Operating	Operating System (OS)	1
OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 relative to Microsoft's new Windows 3.1 operating environment, the two companies severed the relationship in 1992 and OS/2 development fell to IBM exclusively. The name stands for "Operating System/2", because it was introduced as part of the same generation change release as IBM's "Personal System/2 (PS/2)" line of second-generation personal computers. The first version of OS/2 was released in December 1987 and newer versions were released until December 2001. OS/2 was intended as a protected-mode successor of PC DOS. Notably, basic system calls were modeled after MS-DOS calls; their names even started with "Dos" and it was possible to create "Family Mode" applications – text mode applications that could work on both systems. Because of this heritage, OS/2 shares similarities with Unix, Xenix, and Windows NT. IBM discontinued its support for OS/2 on 31 December 2006. Since then, OS/2 has been developed, supported and sold by two different third-party vendors under license from IBM – first by Serenity Systems as eComStation since 2001, and later by Arca Noae LLC as ArcaOS since 2017. Development history 1985–1989: Joint development The development of OS/2 began when IBM and Microsoft signed the "Joint Development Agreement" in August 1985. It was code-named "CP/DOS" and it took two years for the first product to be delivered. OS/2 1.0 was announced in April 1987 and released in December. The original release is textmode-only, and a GUI was introduced with OS/2 1.1 about a year later. OS/2 features an API for controlling the video display (VIO) and handling keyboard and mouse events so that programmers writing for protected-mode need not call the BIOS or access hardware directly. Other development tools included a subset of the video and keyboard APIs as linkable libraries so that family mode programs are able to run under MS-DOS, and, in the OS/2 Extended Edition v1.0, a database engine called Database Manager or DBM (this was related to DB2, and should not be confused with the DBM family of database engines for Unix and Unix-like operating systems). A task-switcher named Program Selector was available through the Ctrl-Esc hotkey combination, allowing the user to select among multitasked text-mode sessions (or screen groups; each can run multiple programs). Communications and database-oriented extensions were delivered in 1988, as part of OS/2 1.0 Extended Edition: SNA, X.25/APPC/LU 6.2, LAN Manager, Query Manager, SQL. The promised user interface, Presentation Manager, was introduced with OS/2 1.1 in October 1988. It had a similar user interface to Windows 2.1, which was released in May of that year. (The interface was replaced in versions 1.2 and 1.3 by a look closer in appearance to Windows 3.0). The Extended Edition of 1.1, sold only through IBM sales channels, introduced distributed database support to IBM database systems and SNA communications support to IBM mainframe networks. In 1989, Version 1.2 introduced Installable Filesystems and, notably, the HPFS filesystem. HPFS provided a number of improvements over the older FAT file system, including long filenames and a form of alternate data streams called Extended Attributes. In addition, extended attributes were also added to the FAT file system. The Extended Edition of 1.2 introduced TCP/IP and Ethernet support. OS/2- and Windows-related books of the late 1980s acknowledged the existence of both systems and promoted OS/2 as the system of the future. 1990: Breakup The collaboration between IBM and Microsoft unravelled in 1990, between the releases of Windows 3.0 and OS/2 1.3. During this time, Windows 3.0 became a tremendous success, selling millions of copies in its first year. Much of its success was because Windows 3.0 (along with MS-DOS) was bundled with most new computers. OS/2, on the other hand, was available only as an additional stand-alone software package. In addition, OS/2 lacked device drivers for many common devices such as printers, particularly non-IBM hardware. Windows, on the other hand, supported a much larger variety of hardware. The increasing popularity of Windows prompted Microsoft to shift its development focus from cooperating on OS/2 with IBM to building its own business based on Windows. Several technical and practical reasons contributed to this breakup. The two companies had significant differences in culture and vision. Microsoft favored the open hardware system approach that contributed to its success on the PC. IBM sought to use OS/2 to drive sales of its own hardware, and urged Microsoft to drop features, such as fonts, that IBM's hardware did not support. Microsoft programmers also became frustrated with IBM's bureaucracy and its use of lines of code to measure programmer productivity. IBM developers complained about the terseness and lack of comments in Microsoft's code, while Microsoft developers complained that IBM's code was bloated. The two products have significant differences in API. OS/2 was announced when Windows 2.0 was near completion, and the Windows API already defined. However, IBM requested that this API be significantly changed for OS/2. Therefore, issues surrounding application compatibility appeared immediately. OS/2 designers hoped for source code conversion tools, allowing complete migration of Windows application source code to OS/2 at some point. However, OS/2 1.x did not gain enough momentum to allow vendors to avoid developing for both OS/2 and Windows in parallel. OS/2 1.x targets the Intel 80286 processor and DOS fundamentally doesn't. IBM insisted on supporting the 80286 processor, with its 16-bit segmented memory mode, because of commitments made to customers who had purchased many 80286-based PS/2s as a result of IBM's promises surrounding OS/2. Until release 2.0 in April 1992, OS/2 ran in 16-bit protected mode and therefore could not benefit from the Intel 80386's much simpler 32-bit flat memory model and virtual 8086 mode features. This was especially painful in providing support for DOS applications. While, in 1988, Windows/386 2.1 could run several cooperatively multitasked DOS applications, including expanded memory (EMS) emulation, OS/2 1.3, released in 1991, was still limited to one "DOS box". Given these issues, Microsoft started to work in parallel on a version of Windows which was more future-oriented and more portable. The hiring of Dave Cutler, former VAX/VMS architect, in 1988 created an immediate competition with the OS/2 team, as Cutler did not think much of the OS/2 technology and wanted to build on his work on the MICA project at Digital rather than creating a "DOS plus". His NT OS/2 was a completely new architecture. IBM grew concerned about the delays in development of OS/2 2.0. Initially, the companies agreed that IBM would take over maintenance of OS/2 1.0 and development of OS/2 2.0, while Microsoft would continue development of OS/2 3.0. In the end, Microsoft decided to recast NT OS/2 3.0 as Windows NT, leaving all future OS/2 development to IBM. From a business perspective, it was logical to concentrate on a consumer line of operating systems based on DOS and Windows, and to prepare a new high-end system in such a way as to keep good compatibility with existing Windows applications. While it waited for this new high-end system to develop, Microsoft would still receive licensing money from Xenix and OS/2 sales. Windows NT's OS/2 heritage can be seen in its initial support for the HPFS filesystem, text mode OS/2 1.x applications, and OS/2 LAN Manager network support. Some early NT materials even included OS/2 copyright notices embedded in the software. One example of NT OS/2 1.x support is in the WIN2K resource kit. Windows NT could also support OS/2 1.x Presentation Manager and AVIO applications with the addition of the Windows NT Add-On Subsystem for Presentation Manager. 1992: 32-bit era OS/2 2.0 was released in April 1992. At the time, the suggested retail price was U.S. $195, while Windows retailed for $150. OS/2 2.0 provided a 32-bit API for native programs, though the OS itself still contained some 16-bit code and drivers. It also included a new OOUI (object-oriented user interface) called the Workplace Shell. This was a fully object-oriented interface that was a significant departure from the previous GUI. Rather than merely providing an environment for program windows (such as the Program Manager), the Workplace Shell provided an environment in which the user could manage programs, files and devices by manipulating objects on the screen. With the Workplace Shell, everything in the system is an "object" to be manipulated. DOS compatibility OS/2 2.0 was touted by IBM as "a better DOS than DOS and a better Windows than Windows". It managed this by including the fully-licensed MS-DOS 5.0, which had been patched and improved upon. For the first time, OS/2 was able to run more than one DOS application at a time. This was so effective, that it allowed OS/2 to run a modified copy of Windows 3.0, itself a DOS extender, including Windows 3.0 applications. Because of the limitations of the Intel 80286 processor, OS/2 1.x could run only one DOS program at a time, and did this in a way that allowed the DOS program to have total control over the computer. A problem in DOS mode could crash the entire computer. In contrast, OS/2 2.0 could leverage the virtual 8086 mode of the Intel 80386 processor to create a much safer virtual machine in which to run DOS programs. This included an extensive set of configuration options to optimize the performance and capabilities given to each DOS program. Any real-mode operating system (such as 8086 Xenix) could also be made to run using OS/2's virtual machine capabilities, subject to certain direct hardware access limitations. Like most 32-bit environments, OS/2 could not run protected-mode DOS programs using the older VCPI interface, unlike the Standard mode of Windows 3.1; it only supported programs written according to DPMI. (Microsoft discouraged the use of VCPI under Windows 3.1, however, due to performance degradation.) Unlike Windows NT, OS/2 always allowed DOS programs the possibility of masking real hardware interrupts, so any DOS program could deadlock the machine in this way. OS/2 could, however, use a hardware watchdog on selected machines (notably IBM machines) to break out of such a deadlock. Later, release 3.0 leveraged the enhancements of newer Intel 80486 and Intel Pentium processors—the Virtual Interrupt Flag (VIF), which was part of the Virtual Mode Extensions (VME)—to solve this problem. Windows 3.x compatibility Compatibility with Windows 3.0 (and later Windows 3.1) was achieved by adapting Windows user-mode code components to run inside a virtual DOS machine (VDM). Originally, a nearly complete version of Windows code was included with OS/2 itself: Windows 3.0 in OS/2 2.0, and Windows 3.1 in OS/2 2.1. Later, IBM developed versions of OS/2 that would use whatever Windows version the user had installed previously, patching it on the fly, and sparing the cost of an additional Windows license. It could either run full-screen, using its own set of video drivers, or "seamlessly," where Windows programs would appear directly on the OS/2 desktop. The process containing Windows was given fairly extensive access to hardware, especially video, and the result was that switching between a full-screen WinOS/2 session and the Workplace Shell could occasionally cause issues. Because OS/2 only runs the user-mode system components of Windows, it is incompatible with Windows device drivers (VxDs) and applications that require them. Multiple Windows applications run by default in a single Windows session – multitasking cooperatively and without memory protection – just as they would under native Windows 3.x. However, to achieve true isolation between Windows 3.x programs, OS/2 can also run multiple copies of Windows in parallel, with each copy residing in a separate VDM. The user can then optionally place each program either in its own Windows session – with preemptive multitasking and full memory protection between sessions, though not within them – or allow some applications to run together cooperatively in a shared Windows session while isolating other applications in one or more separate Windows sessions. At the cost of additional hardware resources, this approach can protect each program in any given Windows session (and each instance of Windows itself) from every other program running in any separate Windows session (though not from other programs running in the same Windows session). Whether Windows applications are running in full-screen or windowed mode, and in one Windows session or several, it is possible to use DDE between OS/2 and Windows applications, and OLE between Windows applications only. 1994: OS/2 Warp Released in 1994, OS/2 version 3.0 was labelled as OS/2 Warp to highlight the new performance benefits, and generally to freshen the product image. "Warp" had originally been the internal IBM name for the release: IBM claimed that it had used Star Trek terms as internal names for prior OS/2 releases, and that this one seemed appropriate for external use as well. At the launch of OS/2 Warp in 1994, Patrick Stewart was to be the Master of Ceremonies; however Kate Mulgrew of the then-upcoming series Star Trek: Voyager substituted him at the last minute. OS/2 Warp offers a host of benefits over OS/2 2.1, notably broader hardware support, greater multimedia capabilities, Internet-compatible networking, and it includes a basic office application suite known as IBM Works. It was released in two versions: the less expensive "Red Spine" and the more expensive "Blue Spine" (named for the color of their boxes). "Red Spine" was designed to support Microsoft Windows applications by utilizing any existing installation of Windows on the computer's hard drive. "Blue Spine" includes Windows support in its own installation, and so can support Windows applications without a Windows installation. As most computers were sold with Microsoft Windows pre-installed and the price was less, "Red Spine" was the more popular product. OS/2 Warp Connect—which has full LAN client support built-in—followed in mid-1995. Warp Connect was nicknamed "Grape". In OS/2 2.0, most performance-sensitive subsystems, including the graphics (Gre) and multimedia (MMPM/2) systems, were updated to 32-bit code in a fixpack, and included as part of OS/2 2.1. Warp 3 brought about a fully 32-bit windowing system, while Warp 4 introduced the object-oriented 32-bit GRADD display driver model. 1996: Warp 4 In 1996, Warp 4 added Java and speech recognition software. IBM also released server editions of Warp 3 and Warp 4 which bundled IBM's LAN Server product directly into the operating system installation. A personal version of Lotus Notes was also included, with a number of template databases for contact management, brainstorming, and so forth. The UK-distributed free demo CD-ROM of OS/2 Warp essentially contained the entire OS and was easily, even accidentally, cracked, meaning that even people who liked it did not have to buy it. This was seen as a backdoor tactic to increase the number of OS/2 users, in the belief that this would increase sales and demand for third-party applications, and thus strengthen OS/2's desktop numbers. This suggestion was bolstered by the fact that this demo version had replaced another which was not so easily cracked, but which had been released with trial versions of various applications. In 2000, the July edition of Australian Personal Computer magazine bundled software CD-ROMs, included a full version of Warp 4 that required no activation and was essentially a free release. Special versions of OS/2 2.11 and Warp 4 also included symmetric multiprocessing (SMP) support. OS/2 sales were largely concentrated in networked computing used by corporate professionals; however, by the early 1990s, it was overtaken by Microsoft Windows NT. While OS/2 was arguably technically superior to Microsoft Windows 95, OS/2 failed to develop much penetration in the consumer and stand-alone desktop PC segments; there were reports that it could not be installed properly on IBM's own Aptiva series of home PCs. Microsoft made an offer in 1994 where IBM would receive the same terms as Compaq (the largest PC manufacturer at the time) for a license of Windows 95, if IBM ended development of OS/2 completely. IBM refused and instead went with an "IBM First" strategy of promoting OS/2 Warp and disparaging Windows, as IBM aimed to drive sales of its own software as well as hardware. By 1995, Windows 95 negotiations between IBM and Microsoft, which were already difficult, stalled when IBM purchased Lotus SmartSuite, which would have directly competed with Microsoft Office. As a result of the dispute, IBM signed the license agreement 15 minutes before Microsoft's Windows 95 launch event, which was later than their competitors and this badly hurt sales of IBM PCs. IBM officials later conceded that OS/2 would not have been a viable operating system to keep them in the PC business. Workplace OS In 1991, IBM started development on an intended replacement for OS/2 called Workplace OS. This was an entirely new product, brand new code, that borrowed only a few sections of code from both the existing OS/2 and AIX products. It used an entirely new microkernel code base, intended (eventually) to host several of IBM's operating systems (including OS/2) as microkernel "personalities". It also included major new architectural features including a system registry, JFS, support for UNIX graphics libraries, and a new driver model. Workplace OS was developed solely for POWER platforms, and IBM intended to market a full line of PowerPCs in an effort to take over the market from Intel. A mission was formed to create prototypes of these machines and they were disclosed to several corporate customers, all of whom raised issues with the idea of dropping Intel. Advanced plans for the new code base would eventually include replacement of the OS/400 operating system by Workplace OS, as well as a microkernel product that would have been used in industries such as telecommunications and set-top television receivers. A partially functional pre-alpha version of Workplace OS was demonstrated at Comdex, where a bemused Bill Gates stopped by the booth. The second and last time it would be shown in public was at an OS/2 user group in Phoenix, Arizona; the pre-alpha code refused to boot. It was released in 1995. But with $990 million being spent per year on development of this as well as Workplace OS, and no possible profit or widespread adoption, the end of the entire Workplace OS and OS/2 product line was near. Downsizing A project was launched internally by IBM to evaluate the looming competitive situation with Microsoft Windows 95. Primary concerns included the major code quality issues in the existing OS/2 product (resulting in over 20 service packs, each requiring more diskettes than the original installation), and the ineffective and heavily matrixed development organization in Boca Raton (where the consultants reported that "basically, everybody reports to everybody") and Austin. That study, tightly classified as "Registered Confidential" and printed only in numbered copies, identified untenable weaknesses and failures across the board in the Personal Systems Division as well as across IBM as a whole. This resulted in a decision being made at a level above the Division to cut over 95% of the overall budget for the entire product line, end all new development (including Workplace OS), eliminate the Boca Raton development lab, end all sales and marketing efforts of the product, and lay off over 1,300 development individuals (as well as sales and support personnel). $990 million had been spent in the last full year. Warp 4 became the last distributed version of OS/2. 2001: Fading out A small and dedicated community remained faithful to OS/2 for many years after its final mainstream release, but overall, OS/2 failed to catch on in the mass market and is little used outside certain niches where IBM traditionally had a stronghold. For example, many bank installations, especially automated teller machines, run OS/2 with a customized user interface; French SNCF national railways used OS/2 1.x in thousands of ticket selling machines. Telecom companies such as Nortel used OS/2 in some voicemail systems. Also, OS/2 was used for the host PC used to control the Satellite Operations Support System equipment installed at NPR member stations from 1994 to 2007, and used to receive the network's programming via satellite. Although IBM began indicating shortly after the release of Warp 4 that OS/2 would eventually be withdrawn, the company did not end support until December 31, 2006. Sales of OS/2 stopped on December 23, 2005. The latest IBM OS/2 Warp version is 4.52, which was released for both desktop and server systems in December 2001. IBM is still delivering defect support for a fee. IBM urges customers to migrate their often highly complex applications to e-business technologies such as Java in a platform-neutral manner. Once application migration is completed, IBM recommends migration to a different operating system, suggesting Linux as an alternative. Third-party development After IBM discontinued development of OS/2, various third parties approached IBM to take over future development of the operating system. The OS/2 software vendor Stardock made such a proposal to IBM in 1999, but it was not followed through by the company. Serenity Systems succeeded in negotiating an agreement with IBM, and began reselling OS/2 as eComStation in 2001. eComStation is now sold by XEU.com, the most recent version (2.1) was released in 2011. In 2015, Arca Noae, LLC announced that they had secured an agreement with IBM to resell OS/2. They released the first version of their OS/2-based operating system in 2017 as ArcaOS. As of 2021, there have been multiple releases of ArcaOS, and it remains under active development. Petitions for open source Many people hoped that IBM would release OS/2 or a significant part of it as open source. Petitions were held in 2005 and 2007, but IBM refused them, citing legal and technical reasons. It is unlikely that the entire OS will be open at any point in the future because it contains third-party code to which IBM does not have copyright, and much of this code is from Microsoft. IBM also once engaged in a technology transfer with Commodore, licensing Amiga technology for OS/2 2.0 and above, in exchange for the REXX scripting language. This means that OS/2 may have some code that was not written by IBM, which can therefore prevent the OS from being re-announced as open-sourced in the future. On the other hand, IBM donated Object REXX for Windows and OS/2 to the Open Object REXX project maintained by the REXX Language Association on SourceForge. There was a petition, arranged by OS2World, to open parts of the OS. Open source operating systems such as Linux have already profited from OS/2 indirectly through IBM's release of the improved JFS file system, which was ported from the OS/2 code base. As IBM didn't release the source of the OS/2 JFS driver, developers ported the Linux driver back to eComStation and added the functionality to boot from a JFS partition. This new JFS driver has been integrated into eComStation v2.0, and later into ArcaOS 5.0. Summary of releases Release dates refer to the US English editions unless otherwise noted. Features and technology User interface The graphic system has a layer named Presentation Manager that manages windows, fonts, and icons. This is similar in functionality to a non-networked version of X11 or the Windows GDI. On top of this lies the Workplace Shell (WPS) introduced in OS/2 2.0. WPS is an object-oriented shell allowing the user to perform traditional computing tasks such as accessing files, printers, launching legacy programs, and advanced object oriented tasks using built-in and third-party application objects that extended the shell in an integrated fashion not available on any other mainstream operating system. WPS follows IBM's Common User Access user interface standards. WPS represents objects such as disks, folders, files, program objects, and printers using the System Object Model (SOM), which allows code to be shared among applications, possibly written in different programming languages. A distributed version called DSOM allowed objects on different computers to communicate. DSOM is based on CORBA. The object oriented aspect of SOM is similar to, and a direct competitor to, Microsoft's Component Object Model, though it is implemented in a radically different manner; for instance, one of the most notable differences between SOM and COM is SOM's support for inheritance (one of the most fundamental concepts of OO programming)—COM does not have such support. SOM and DSOM are no longer being developed. The multimedia capabilities of OS/2 are accessible through Media Control Interface commands. The last update (bundled with the IBM version of Netscape Navigator plugins) added support for MPEG files. Support for newer formats such as PNG, progressive JPEG, DivX, Ogg, and MP3 comes from third parties. Sometimes it is integrated with the multimedia system, but in other offers it comes as standalone applications. Commands The following list of commands is supported by cmd.exe on OS/2. ansi append assign attrib backup boot break cache call cd chcp chdir chkdsk cls cmd codepage command comp copy createdd date ddinstal debug del detach dir diskcomp diskcopy doskey dpath eautil echo endlocal erase exit extproc fdisk fdiskpm find for format fsaccess goto graftabl help if join keyb keys label makeini md mem mkdir mode more move patch path pause picview pmrexx print prompt pstat rd recover rem ren rename replace restore rmdir set setboot setcom40 setlocal share shift sort spool start subst syslevel syslog time trace tracebuf tracefmt tree type undelete unpack ver verify view vmdisk vol xcopy Networking The TCP/IP stack is based on the open source BSD stack as visible with SCCS what compatible tools. IBM included tools such as ftp and telnet and even servers for both commands. IBM sold several networking extensions including NFS support and an X11 server. Drivers Hardware vendors were reluctant to support device drivers for alternative operating systems including OS/2, leaving users with few choices from a select few vendors. To relieve this issue for video cards, IBM licensed a reduced version of the Scitech display drivers, allowing users to choose from a wide selection of cards supported through Scitech's modular driver design. Virtualization OS/2 has historically been more difficult to run in a virtual machine than most other legacy x86 operating systems because of its extensive reliance on the full set of features of the x86 CPU; in particular, OS/2's use of ring 2 prevented it from running in early versions of VMware. Newer versions of VMware provide official support for OS/2, specifically for eComStation. VirtualPC from Microsoft (originally Connectix) has been able to run OS/2 without hardware virtualization support for many years. It also provided "additions" code which greatly improves host–guest OS interactions in OS/2. The additions are not provided with the current version of VirtualPC, but the version last included with a release may still be used with current releases. At one point, OS/2 was a supported host for VirtualPC in addition to a guest. Note that OS/2 runs only as a guest on those versions of VirtualPC that use virtualization (x86 based hosts) and not those doing full emulation (VirtualPC for Mac). VirtualBox from Oracle Corporation (originally InnoTek, later Sun) supports OS/2 1.x, Warp 3 through 4.5, and eComStation as well as "Other OS/2" as guests. However, attempting to run OS/2 and eComStation can still be difficult, if not impossible, because of the strict requirements of VT-x/AMD-V hardware-enabled virtualization and only ACP2/MCP2 is reported to work in a reliable manner. ArcaOS supports being run as a virtual machine guest inside VirtualBox, VMware ESXi and VMWare Workstation. It ships with VirtualBox Guest Additions, and driver improvements to improve performance as a guest operating system. The difficulties in efficiently running OS/2 have, at least once, created an opportunity for a new virtualization company. A large bank in Moscow needed a way to use OS/2 on newer hardware that OS/2 did not support. As virtualization software is an easy way around this, the company desired to run OS/2 under a hypervisor. Once it was determined that VMware was not a possibility, it hired a group of Russian software developers to write a host-based hypervisor that would officially support OS/2. Thus, the Parallels, Inc. company and their Parallels Workstation product was born. Security niche OS/2 has few native computer viruses; while it is not invulnerable by design, its reduced market share appears to have discouraged virus writers. There are, however, OS/2-based antivirus programs, dealing with DOS viruses and Windows viruses that could pass through an OS/2 server. Problems Some problems were classic subjects of comparison with other operating systems: Synchronous input queue (SIQ): if a GUI application was not servicing its window messages, the entire GUI system could get stuck and a reboot was required. This problem was considerably reduced with later Warp 3 fixpacks and refined by Warp 4, by taking control over the application after it had not responded for several seconds. No unified object handles (OS/2 v2.11 and earlier): The availability of threads probably led system designers to overlook mechanisms which allow a single thread to wait for different types of asynchronous events at the same time, for example the keyboard and the mouse in a "console" program. Even though select was added later, it only worked on network sockets. In case of a console program, dedicating a separate thread for waiting on each source of events made it difficult to properly release all the input devices before starting other programs in the same "session". As a result, console programs usually polled the keyboard and the mouse alternately, which resulted in wasted CPU and a characteristic "jerky" reactivity to user input. In OS/2 3.0 IBM introduced a new call for this specific problem. Historical uses OS/2 has been widely used in Iran Export Bank (Bank Saderat Iran) in their teller machines, ATMs and local servers (over 30,000 working stations). As of 2011, the bank moved to virtualize and renew their infrastructure by moving OS/2 to Virtual Machines running over Windows. OS/2 was widely used in Brazilian banks. Banco do Brasil had a peak 10,000 machines running OS/2 Warp in the 1990s. OS/2 was used in automated teller machines until 2006. The workstations and automated teller machines and attendant computers have been migrated to Linux. OS/2 has been used in the banking industry. Suncorp bank in Australia still ran its ATM network on OS/2 as late as 2002. ATMs at Perisher Blue used OS/2 as late as 2009, and even the turn of the decade. OS/2 was widely adopted by accounting professionals and auditing companies. In mid-1990s native 32-bit accounting software were well developed and serving corporate markets. OS/2 ran the faulty baggage handling system at Denver International Airport. The OS was eventually scrapped, but the software written for the system led to massive delays in the opening of the new airport. The OS itself was not at fault, but the software written to run on the OS was. The baggage handling system was eventually removed. OS/2 was used by radio personality Howard Stern. He once had a 10-minute on-air rant about OS/2 versus Windows 95 and recommended OS/2. He also used OS/2 on his IBM 760CD laptop. OS/2 was used as part of the Satellite Operations Support System (SOSS) for NPR's Public Radio Satellite System. SOSS was a computer-controlled system using OS/2 that NPR member stations used to receive programming feeds via satellite. SOSS was introduced in 1994 using OS/2 3.0, and was retired in 2007, when NPR switched over to its successor, the ContentDepot. OS/2 was used to control the SkyTrain automated light rail system in Vancouver, Canada until the late 2000s when it was replaced by Windows XP. OS/2 was used in the London Underground Jubilee Line Extension Signals Control System (JLESCS) in London, England. This control system delivered by Alcatel was in use from 1999 to 2011 i.e. between abandonment before opening of the line's unimplemented original automatic train control system and the present SelTrac system. JLESCS did not provide automatic train operation only manual train supervision. Six OS/2 local site computers were distributed along the railway between Stratford and Westminster, the shunting tower at Stratford Market Depot, and several formed the central equipment located at Neasden Depot. It was once intended to cover the rest of the line between Green Park and Stanmore but this was never introduced. OS/2 has been used by The Co-operative Bank in the UK for its domestic call centre staff, using a bespoke program created to access customer accounts which cannot easily be migrated to Windows. OS/2 has been used by the Stop & Shop supermarket chain (and has been installed in new stores as recently as March 2010). OS/2 has been used on ticket machines for Tramlink in outer-London. OS/2 has been used in New York City's subway system for MetroCards. Rather than interfacing with the user, it connects simple computers and the mainframes. When NYC MTA finishes its transition to contactless payment, OS/2 will be removed. OS/2 was used in checkout systems at Safeway supermarkets. OS/2 was used by Trenitalia, both for the desktops at Ticket Counters and for the Automatic Ticket Counters up to 2011. Incidentally, the Automatic Ticket Counters with OS/2 were more reliable than the current ones running a flavor of Windows. OS/2 was used as the main operating system for Abbey National General Insurance motor and home direct call centre products using the PMSC Series III insurance platform on DB2.2 from 1996-2001. Awards BYTE in 1989 listed OS/2 as among the "Excellence" winners of the BYTE Awards, stating that it "is today where the Macintosh was in 1984: It's a development platform in search of developers". The magazine predicted that "When it's complete and bug-free, when it can really use the 80386, and when more desktops sport OS/2-capable PCs, OS/2 will—deservedly—supersede DOS. But even as it stands, OS/2 is a milestone product". In March 1995 OS/2 won seven awards InfoWorld Product of the Year. Five Awards at CeBIT. PC Professional Magazine - Innovation of the Year award. CHIP Magazine named OS/2 Warp the Operating System of the Year. DOS International named OS/2 Warp the Operating System of the Year. 1+1 Magazine awarded it with the Software Marketing Quality award. Industrie Forum awarded it with its Design Excellence. SPA Best Business Software Award. IBM products utilizing OS/2 IBM has used OS/2 in a wide variety of hardware products, effectively as a form of embedded operating system. See also History of the graphical user interface Multiple Virtual DOS Machine (MVDM) - OS/2 virtual DOS machine and seamless Windows integration Team OS/2 Windows Libraries for OS/2 LAN Manager References Further reading —Necasek discusses an aborted port to PowerPC machines. External links os2world.com – Community of OS/2 users ecomstation.ru – Community of eComStation and OS/2 users netlabs.org – OpenSource Software for OS/2 and eCS OS/2 FAQ hobbes.nmsu.edu – The OS/2 software repository EDM/2 – The source for OS/2 developers eCSoft/2 – The OS/2 and eComstation software guide osFree an open source project to build an OS/2 clone operating system Voyager Project, a defunct project to reimplement OS/2 on modern technology OS/2 to Linux API porting project Open Source OS/2 API implementation for Windows Microsoft documentation of OS/2 API compatibility with Windows NT The History of OS/2 Technical details of OS/2 OS/2 Warp 4 Installation and Update Manual; with boot disks and many links 1987 software Discontinued operating systems IBM operating systems Legacy systems Star Trek fandom X86 operating systems	Operating System (OS)	2
S-OS S-OS is a simple operating system mainly for Z80 based computers. The operating system was first presented in 1986 in the Japanese magazine Oh!X in an article called "The Sentinel". Commands The command and command set is very simplified. Directory #D [<device name>:] Change default device (S=startup, A=tape..) #DV <device name>: Jump to address (and run program) #J <address> Load the program #L <filename>[:<address>] Enter the machine specific monitor #M Delete the file #K <file name> Save a memory block to file #S <filename>: <start address>: <end address>[: <execution address>] Exit from S-OS and reboot #! Supported systems Sharp MZ-80K/C/1200 Sharp MZ-700 / 1500 Sharp MZ-80B / 2000 / 2200 Sharp MZ-2500/2861(MZ-2500 mode) Sharp X1/C/D/Cs/Ck/F/G/Twin (two different implementations) Sharp X1turbo/II/III/Z/ZII/ZIII NEC PC-8001/8801 NEC PC-6001mkII/6601/SR Sony SMC-777C Toshiba PASOPIA Fujitsu FM-7 / 77 (Z80 extension card) Sharp X68000 (emulated Z80) PC-286/NEC PC-9801 (emulated Z80) MSX 2 / 2+ / turboR Casio FP-1000 / 1100 Windows 32 bit (emulated Z80) Sharp calculators PC-G850/S/V/VS References External links http://www.retropc.net/ohishi/s-os/ http://homepage2.nifty.com/akikawa/sword/index.html http://www16.ocn.ne.jp/~ver0/g800/#sos Microcomputer software ja:Oh!X#THE_SENTINEL	Operating System (OS)	3
Microsoft Windows Microsoft Windows, commonly referred to as Windows, is a group of several proprietary graphical operating system families, all of which are developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. Active Microsoft Windows families include Windows NT and Windows IoT; these may encompass subfamilies, (e.g. Windows Server or Windows Embedded Compact) (Windows CE). Defunct Microsoft Windows families include Windows 9x, Windows Mobile and Windows Phone. Microsoft introduced an operating environment named Windows on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs). Microsoft Windows came to dominate the world's personal computer (PC) market with over 90% market share, overtaking Mac OS, which had been introduced in 1984. Apple came to see Windows as an unfair encroachment on their innovation in GUI development as implemented on products such as the Lisa and Macintosh (eventually settled in court in Microsoft's favor in 1993). On PCs, Windows is still the most popular operating system in all countries. However, in 2014, Microsoft admitted losing the majority of the overall operating system market to Android, because of the massive growth in sales of Android smartphones. In 2014, the number of Windows devices sold was less than 25% that of Android devices sold. This comparison, however, may not be fully relevant, as the two operating systems traditionally target different platforms. Still, numbers for server use of Windows (that are comparable to competitors) show one third market share, similar to that for end user use. , the most recent version of Windows for PCs and tablets is Windows 11, version 21H2. The most recent version for embedded devices is Windows 10, version 21H1. The most recent version for server computers is Windows Server 2022, version 21H2. A specialized version of Windows also runs on the Xbox One and Xbox Series X/S video game consoles. Genealogy By marketing role Microsoft, the developer of Windows, has registered several trademarks, each of which denotes a family of Windows operating systems that target a specific sector of the computing industry. As of 2014, the following Windows families were being actively developed: Windows NT: Started as a family of operating systems with Windows NT 3.1, an operating system for server computers and workstations. It now consists of three operating system subfamilies that are released almost at the same time and share the same kernel: Windows: The operating system for mainstream personal computers and tablets. The latest version is Windows 11. The main competitor of this family is macOS by Apple for personal computers and iPadOS and Android for tablets (c.f. ). Windows Server: The operating system for server computers. The latest version is Windows Server 2022. Unlike its client sibling, it has adopted a strong naming scheme. The main competitor of this family is Linux. (c.f. ) Windows PE: A lightweight version of its Windows sibling, meant to operate as a live operating system, used for installing Windows on bare-metal computers (especially on many computers at once), recovery or troubleshooting purposes. The latest version is Windows PE 10. Windows IoT (previously Windows Embedded): Initially, Microsoft developed Windows CE as a general-purpose operating system for every device that was too resource-limited to be called a full-fledged computer. Eventually, however, Windows CE was renamed Windows Embedded Compact and was folded under Windows Compact trademark which also consists of Windows Embedded Industry, Windows Embedded Professional, Windows Embedded Standard, Windows Embedded Handheld and Windows Embedded Automotive. The following Windows families are no longer being developed: Windows 9x: An operating system that targeted the consumer market. Discontinued because of suboptimal performance. (PC World called its last version, Windows Me, one of the worst products of all time.) Microsoft now caters to the consumer market with Windows NT. Windows Mobile: The predecessor to Windows Phone, it was a mobile phone operating system. The first version was called Pocket PC 2000; the third version, Windows Mobile 2003 is the first version to adopt the Windows Mobile trademark. The last version is Windows Mobile 6.5. Windows Phone: An operating system sold only to manufacturers of smartphones. The first version was Windows Phone 7, followed by Windows Phone 8, and Windows Phone 8.1. It was succeeded by Windows 10 Mobile, that is now also discontinued. Version history The term Windows collectively describes any or all of several generations of Microsoft operating system products. These products are generally categorized as follows: Early versions The history of Windows dates back to 1981 when Microsoft started work on a program called "Interface Manager". It was announced in November 1983 (after the Apple Lisa, but before the Macintosh) under the name "Windows", but Windows 1.0 was not released until November 1985. Windows 1.0 was to compete with Apple's operating system, but achieved little popularity. Windows 1.0 is not a complete operating system; rather, it extends MS-DOS. The shell of Windows 1.0 is a program known as the MS-DOS Executive. Components included Calculator, Calendar, Cardfile, Clipboard Viewer, Clock, Control Panel, Notepad, Paint, Reversi, Terminal and Write. Windows 1.0 does not allow overlapping windows. Instead all windows are tiled. Only modal dialog boxes may appear over other windows. Microsoft sold as included Windows Development libraries with the C development environment, which included numerous windows samples. Windows 2.0 was released in December 1987, and was more popular than its predecessor. It features several improvements to the user interface and memory management. Windows 2.03 changed the OS from tiled windows to overlapping windows. The result of this change led to Apple Computer filing a suit against Microsoft alleging infringement on Apple's copyrights. Windows 2.0 also introduced more sophisticated keyboard shortcuts and could make use of expanded memory. Windows 2.1 was released in two different versions: Windows/286 and Windows/386. Windows/386 uses the virtual 8086 mode of the Intel 80386 to multitask several DOS programs and the paged memory model to emulate expanded memory using available extended memory. Windows/286, in spite of its name, runs on both Intel 8086 and Intel 80286 processors. It runs in real mode but can make use of the high memory area. In addition to full Windows-packages, there were runtime-only versions that shipped with early Windows software from third parties and made it possible to run their Windows software on MS-DOS and without the full Windows feature set. The early versions of Windows are often thought of as graphical shells, mostly because they ran on top of MS-DOS and use it for file system services. However, even the earliest Windows versions already assumed many typical operating system functions; notably, having their own executable file format and providing their own device drivers (timer, graphics, printer, mouse, keyboard and sound). Unlike MS-DOS, Windows allowed users to execute multiple graphical applications at the same time, through cooperative multitasking. Windows implemented an elaborate, segment-based, software virtual memory scheme, which allows it to run applications larger than available memory: code segments and resources are swapped in and thrown away when memory became scarce; data segments moved in memory when a given application had relinquished processor control. Windows 3.x Windows 3.0, released in 1990, improved the design, mostly because of virtual memory and loadable virtual device drivers (VxDs) that allow Windows to share arbitrary devices between multi-tasked DOS applications. Windows 3.0 applications can run in protected mode, which gives them access to several megabytes of memory without the obligation to participate in the software virtual memory scheme. They run inside the same address space, where the segmented memory provides a degree of protection. Windows 3.0 also featured improvements to the user interface. Microsoft rewrote critical operations from C into assembly. Windows 3.0 is the first Microsoft Windows version to achieve broad commercial success, selling 2 million copies in the first six months. Windows 3.1, made generally available on March 1, 1992, featured a facelift. In August 1993, Windows for Workgroups, a special version with integrated peer-to-peer networking features and a version number of 3.11, was released. It was sold along with Windows 3.1. Support for Windows 3.1 ended on December 31, 2001. Windows 3.2, released 1994, is an updated version of the Chinese version of Windows 3.1. The update was limited to this language version, as it fixed only issues related to the complex writing system of the Chinese language. Windows 3.2 was generally sold by computer manufacturers with a ten-disk version of MS-DOS that also had Simplified Chinese characters in basic output and some translated utilities. Windows 9x The next major consumer-oriented release of Windows, Windows 95, was released on August 24, 1995. While still remaining MS-DOS-based, Windows 95 introduced support for native 32-bit applications, plug and play hardware, preemptive multitasking, long file names of up to 255 characters, and provided increased stability over its predecessors. Windows 95 also introduced a redesigned, object oriented user interface, replacing the previous Program Manager with the Start menu, taskbar, and Windows Explorer shell. Windows 95 was a major commercial success for Microsoft; Ina Fried of CNET remarked that "by the time Windows 95 was finally ushered off the market in 2001, it had become a fixture on computer desktops around the world." Microsoft published four OEM Service Releases (OSR) of Windows 95, each of which was roughly equivalent to a service pack. The first OSR of Windows 95 was also the first version of Windows to be bundled with Microsoft's web browser, Internet Explorer. Mainstream support for Windows 95 ended on December 31, 2000, and extended support for Windows 95 ended on December 31, 2001. Windows 95 was followed up with the release of Windows 98 on June 25, 1998, which introduced the Windows Driver Model, support for USB composite devices, support for ACPI, hibernation, and support for multi-monitor configurations. Windows 98 also included integration with Internet Explorer 4 through Active Desktop and other aspects of the Windows Desktop Update (a series of enhancements to the Explorer shell which were also made available for Windows 95). In May 1999, Microsoft released Windows 98 Second Edition, an updated version of Windows 98. Windows 98 SE added Internet Explorer 5.0 and Windows Media Player 6.2 amongst other upgrades. Mainstream support for Windows 98 ended on June 30, 2002, and extended support for Windows 98 ended on July 11, 2006. On September 14, 2000, Microsoft released Windows Me (Millennium Edition), the last DOS-based version of Windows. Windows Me incorporated visual interface enhancements from its Windows NT-based counterpart Windows 2000, had faster boot times than previous versions (which however, required the removal of the ability to access a real mode DOS environment, removing compatibility with some older programs), expanded multimedia functionality (including Windows Media Player 7, Windows Movie Maker, and the Windows Image Acquisition framework for retrieving images from scanners and digital cameras), additional system utilities such as System File Protection and System Restore, and updated home networking tools. However, Windows Me was faced with criticism for its speed and instability, along with hardware compatibility issues and its removal of real mode DOS support. PC World considered Windows Me to be one of the worst operating systems Microsoft had ever released, and the 4th worst tech product of all time. Windows NT Version history Early versions (Windows NT 3.1/3.5/3.51/4.0/2000) In November 1988, a new development team within Microsoft (which included former Digital Equipment Corporation developers Dave Cutler and Mark Lucovsky) began work on a revamped version of IBM and Microsoft's OS/2 operating system known as "NT OS/2". NT OS/2 was intended to be a secure, multi-user operating system with POSIX compatibility and a modular, portable kernel with preemptive multitasking and support for multiple processor architectures. However, following the successful release of Windows 3.0, the NT development team decided to rework the project to use an extended 32-bit port of the Windows API known as Win32 instead of those of OS/2. Win32 maintained a similar structure to the Windows APIs (allowing existing Windows applications to easily be ported to the platform), but also supported the capabilities of the existing NT kernel. Following its approval by Microsoft's staff, development continued on what was now Windows NT, the first 32-bit version of Windows. However, IBM objected to the changes, and ultimately continued OS/2 development on its own. Windows NT was the first Windows operating system based on a hybrid kernel. The hybrid kernel was designed as a modified microkernel, influenced by the Mach microkernel developed by Richard Rashid at Carnegie Mellon University, but without meeting all of the criteria of a pure microkernel. The first release of the resulting operating system, Windows NT 3.1 (named to associate it with Windows 3.1) was released in July 1993, with versions for desktop workstations and servers. Windows NT 3.5 was released in September 1994, focusing on performance improvements and support for Novell's NetWare, and was followed up by Windows NT 3.51 in May 1995, which included additional improvements and support for the PowerPC architecture. Windows NT 4.0 was released in June 1996, introducing the redesigned interface of Windows 95 to the NT series. On February 17, 2000, Microsoft released Windows 2000, a successor to NT 4.0. The Windows NT name was dropped at this point in order to put a greater focus on the Windows brand. Windows XP The next major version of Windows NT, Windows XP, was released on October 25, 2001. The introduction of Windows XP aimed to unify the consumer-oriented Windows 9x series with the architecture introduced by Windows NT, a change which Microsoft promised would provide better performance over its DOS-based predecessors. Windows XP would also introduce a redesigned user interface (including an updated Start menu and a "task-oriented" Windows Explorer), streamlined multimedia and networking features, Internet Explorer 6, integration with Microsoft's .NET Passport services, a "compatibility mode" to help provide backwards compatibility with software designed for previous versions of Windows, and Remote Assistance functionality. At retail, Windows XP was now marketed in two main editions: the "Home" edition was targeted towards consumers, while the "Professional" edition was targeted towards business environments and power users, and included additional security and networking features. Home and Professional were later accompanied by the "Media Center" edition (designed for home theater PCs, with an emphasis on support for DVD playback, TV tuner cards, DVR functionality, and remote controls), and the "Tablet PC" edition (designed for mobile devices meeting its specifications for a tablet computer, with support for stylus pen input and additional pen-enabled applications). Mainstream support for Windows XP ended on April 14, 2009. Extended support ended on April 8, 2014. After Windows 2000, Microsoft also changed its release schedules for server operating systems; the server counterpart of Windows XP, Windows Server 2003, was released in April 2003. It was followed in December 2005, by Windows Server 2003 R2. Windows Vista After a lengthy development process, Windows Vista was released on November 30, 2006, for volume licensing and January 30, 2007, for consumers. It contained a number of new features, from a redesigned shell and user interface to significant technical changes, with a particular focus on security features. It was available in a number of different editions, and has been subject to some criticism, such as drop of performance, longer boot time, criticism of new UAC, and stricter license agreement. Vista's server counterpart, Windows Server 2008 was released in early 2008. Windows 7 On July 22, 2009, Windows 7 and Windows Server 2008 R2 were released as RTM (release to manufacturing) while the former was released to the public 3 months later on October 22, 2009. Unlike its predecessor, Windows Vista, which introduced a large number of new features, Windows 7 was intended to be a more focused, incremental upgrade to the Windows line, with the goal of being compatible with applications and hardware with which Windows Vista was already compatible. Windows 7 has multi-touch support, a redesigned Windows shell with an updated taskbar with revealable jump lists that contain shortcuts to files frequently used with specific applications and shortcuts to tasks within the application, a home networking system called HomeGroup, and performance improvements. Windows 8 and 8.1 Windows 8, the successor to Windows 7, was released generally on October 26, 2012. A number of significant changes were made on Windows 8, including the introduction of a user interface based around Microsoft's Metro design language with optimizations for touch-based devices such as tablets and all-in-one PCs. These changes include the Start screen, which uses large tiles that are more convenient for touch interactions and allow for the display of continually updated information, and a new class of apps which are designed primarily for use on touch-based devices. The new Windows version required a minimum resolution of 1024×768 pixels, effectively making it unfit for netbooks with 800×600-pixel screens. Other changes include increased integration with cloud services and other online platforms (such as social networks and Microsoft's own OneDrive (formerly SkyDrive) and Xbox Live services), the Windows Store service for software distribution, and a new variant known as Windows RT for use on devices that utilize the ARM architecture, and a new keyboard shortcut for screenshots. An update to Windows 8, called Windows 8.1, was released on October 17, 2013, and includes features such as new live tile sizes, deeper OneDrive integration, and many other revisions. Windows 8 and Windows 8.1 have been subject to some criticism, such as removal of the Start menu. Windows 10 On September 30, 2014, Microsoft announced Windows 10 as the successor to Windows 8.1. It was released on July 29, 2015, and addresses shortcomings in the user interface first introduced with Windows 8. Changes on PC include the return of the Start Menu, a virtual desktop system, and the ability to run Windows Store apps within windows on the desktop rather than in full-screen mode. Windows 10 is said to be available to update from qualified Windows 7 with SP1, Windows 8.1 and Windows Phone 8.1 devices from the Get Windows 10 Application (for Windows 7, Windows 8.1) or Windows Update (Windows 7). In February 2017, Microsoft announced the migration of its Windows source code repository from Perforce to Git. This migration involved 3.5 million separate files in a 300 gigabyte repository. By May 2017, 90 percent of its engineering team was using Git, in about 8500 commits and 1760 Windows builds per day. In June 2021, shortly before Microsoft's announcement of Windows 11, Microsoft updated their lifecycle policy pages for Windows 10, revealing that support for their last release of Windows 10 will be October 14, 2025. Windows 11 On June 24, 2021, Windows 11 was announced as the successor to Windows 10 during a livestream. The new operating system was designed to be more user-friendly and understandable. It was released on October 5, 2021. Windows 11 is a free upgrade to some Windows 10 users as of now. Windows 365 In July 2021, Microsoft announced it will start selling subscriptions to virtualized Windows desktops as part of a new Windows 365 service in the following month. It is not a standalone version of Microsoft Windows, but a web service that provides access to Windows 10 and Windows 11 built on top of Azure Virtual Desktop. The new service will allow for cross-platform usage, aiming to make the operating system available for both Apple and Android users. The subscription-based service will be accessible through any operating system with a web browser. Microsoft has stated that the new service is an attempt at capitalizing on the growing trend, fostered during the COVID-19 pandemic, for businesses to adopt a hybrid work environment, in which "employees split their time between the office and home" according to vice president Jared Spataro. As the service will be accessible through web-browsers, Microsoft will be able to bypass the need to publish the service through Google Play or the Apple App Store. Microsoft announced Windows 365 availability to business and enterprise customers on August 2, 2021. Multilingual support Multilingual support has been built into Windows since Windows 3.0. The language for both the keyboard and the interface can be changed through the Region and Language Control Panel. Components for all supported input languages, such as Input Method Editors, are automatically installed during Windows installation (in Windows XP and earlier, files for East Asian languages, such as Chinese, and right-to-left scripts, such as Arabic, may need to be installed separately, also from the said Control Panel). Third-party IMEs may also be installed if a user feels that the provided one is insufficient for their needs. Interface languages for the operating system are free for download, but some languages are limited to certain editions of Windows. Language Interface Packs (LIPs) are redistributable and may be downloaded from Microsoft's Download Center and installed for any edition of Windows (XP or later) they translate most, but not all, of the Windows interface, and require a certain base language (the language which Windows originally shipped with). This is used for most languages in emerging markets. Full Language Packs, which translates the complete operating system, are only available for specific editions of Windows (Ultimate and Enterprise editions of Windows Vista and 7, and all editions of Windows 8, 8.1 and RT except Single Language). They do not require a specific base language, and are commonly used for more popular languages such as French or Chinese. These languages cannot be downloaded through the Download Center, but available as optional updates through the Windows Update service (except Windows 8). The interface language of installed applications is not affected by changes in the Windows interface language. The availability of languages depends on the application developers themselves. Windows 8 and Windows Server 2012 introduces a new Language Control Panel where both the interface and input languages can be simultaneously changed, and language packs, regardless of type, can be downloaded from a central location. The PC Settings app in Windows 8.1 and Windows Server 2012 R2 also includes a counterpart settings page for this. Changing the interface language also changes the language of preinstalled Windows Store apps (such as Mail, Maps and News) and certain other Microsoft-developed apps (such as Remote Desktop). The above limitations for language packs are however still in effect, except that full language packs can be installed for any edition except Single Language, which caters to emerging markets. Platform support Windows NT included support for several platforms before the x86-based personal computer became dominant in the professional world. Windows NT 4.0 and its predecessors supported PowerPC, DEC Alpha and MIPS R4000 (although some of the platforms implement 64-bit computing, the OS treated them as 32-bit). Windows 2000 dropped support for all platforms, except the third generation x86 (known as IA-32) or newer in 32-bit mode. The client line of Windows NT family still runs on IA-32 but the Windows Server line ceased supporting this platform with the release of Windows Server 2008 R2. With the introduction of the Intel Itanium architecture (IA-64), Microsoft released new versions of Windows to support it. Itanium versions of Windows XP and Windows Server 2003 were released at the same time as their mainstream x86 counterparts. Windows XP 64-Bit Edition, released in 2005, is the last Windows client operating systems to support Itanium. Windows Server line continues to support this platform until Windows Server 2012; Windows Server 2008 R2 is the last Windows operating system to support Itanium architecture. On April 25, 2005, Microsoft released Windows XP Professional x64 Edition and Windows Server 2003 x64 Editions to support x86-64 (or simply x64), the 64-bit version of x86 architecture. Windows Vista was the first client version of Windows NT to be released simultaneously in IA-32 and x64 editions. x64 is still supported. An edition of Windows 8 known as Windows RT was specifically created for computers with ARM architecture and while ARM is still used for Windows smartphones with Windows 10, tablets with Windows RT will not be updated. Starting from Windows 10 Fall Creators Update (version 1709) and later includes support for PCs with ARM architecture. Windows 11 is the first version to drop support for 32-bit hardware. Windows CE Windows CE (officially known as Windows Embedded Compact), is an edition of Windows that runs on minimalistic computers, like satellite navigation systems and some mobile phones. Windows Embedded Compact is based on its own dedicated kernel, dubbed Windows CE kernel. Microsoft licenses Windows CE to OEMs and device makers. The OEMs and device makers can modify and create their own user interfaces and experiences, while Windows CE provides the technical foundation to do so. Windows CE was used in the Dreamcast along with Sega's own proprietary OS for the console. Windows CE was the core from which Windows Mobile was derived. Its successor, Windows Phone 7, was based on components from both Windows CE 6.0 R3 and Windows CE 7.0. Windows Phone 8 however, is based on the same NT-kernel as Windows 8. Windows Embedded Compact is not to be confused with Windows XP Embedded or Windows NT 4.0 Embedded, modular editions of Windows based on Windows NT kernel. Xbox OS Xbox OS is an unofficial name given to the version of Windows that runs on Xbox consoles. From Xbox One onwards it is an implementation with an emphasis on virtualization (using Hyper-V) as it is three operating systems running at once, consisting of the core operating system, a second implemented for games and a more Windows-like environment for applications. Microsoft updates Xbox One's OS every month, and these updates can be downloaded from the Xbox Live service to the Xbox and subsequently installed, or by using offline recovery images downloaded via a PC. It was originally based on NT 6.2 (Windows 8) kernel, and the latest version runs on an NT 10.0 base. This system is sometimes referred to as "Windows 10 on Xbox One" or "OneCore". Xbox One and Xbox Series operating systems also allow limited (due to licensing restrictions and testing resources) backward compatibility with previous generation hardware, and the Xbox 360's system is backwards compatible with the original Xbox. Version control system Before 2017 Microsoft has used a proprietary SourceDepot Version Control system which couldn't keep up with size of Windows. Microsoft had begun to integrate Git into Team Foundation Server in 2013, but Windows continued to rely on Source Depot. The Windows code was divided among 65 different repositories with a kind of virtualization layer to produce unified view of all of the code. In 2017 Microsoft announced that it would start using Git, an open source version control system created by Linus Torvalds and in May 2017 they reported that has completed migration into the Git repository. VFSForGit Because of its large, decades-long history, however, the Windows codebase is not especially well suited to the decentralized nature of Linux development that Git was originally created to manage. Each Git repository contains a complete history of all the files, which proved unworkable for Windows developers because cloning the whole repository takes several hours. Microsoft has been working on a new project called the Virtual File System for Git (VFSForGit) to address these challenges. In 2021 the VFS for Git has been superseded by Scalar. Timeline of releases Usage share and device sales Use of the latest version Windows 10 has exceeded Windows 7 globally since early 2018. For desktop and laptop computers, according to Net Applications and StatCounter, which track the use of operating systems in devices that are active on the Web, Windows was the most used operating-system family in August 2021, with around 91% usage share according to Net Applications and around 76% usage share according to StatCounter. Including personal computers of all kinds (e.g., desktops, laptops, mobile devices, and game consoles), Windows OSes accounted for 32.67% of usage share in August 2021, compared to Android (highest, at 46.03%), iOS's 13.76%, iPadOS's 2.81%, and macOS's 2.51%, according to Net Applications and 30.73% of usage share in August 2021, compared to Android (highest, at 42.56%), iOS/iPadOS's 16.53%, and macOS's 6.51%, according to StatCounter. Those statistics do not include servers (including so-called cloud computing, where Microsoft is known not to be a leader, with Linux used more than Windows), as Net Applications and StatCounter use web browsing as a proxy for all use. Security Consumer versions of Windows were originally designed for ease-of-use on a single-user PC without a network connection, and did not have security features built in from the outset. However, Windows NT and its successors are designed for security (including on a network) and multi-user PCs, but were not initially designed with Internet security in mind as much, since, when it was first developed in the early 1990s, Internet use was less prevalent. These design issues combined with programming errors (e.g. buffer overflows) and the popularity of Windows means that it is a frequent target of computer worm and virus writers. In June 2005, Bruce Schneier's Counterpane Internet Security reported that it had seen over 1,000 new viruses and worms in the previous six months. In 2005, Kaspersky Lab found around 11,000 malicious programs viruses, Trojans, back-doors, and exploits written for Windows. Microsoft releases security patches through its Windows Update service approximately once a month (usually the second Tuesday of the month), although critical updates are made available at shorter intervals when necessary. In versions of Windows after and including Windows 2000 SP3 and Windows XP, updates can be automatically downloaded and installed if the user selects to do so. As a result, Service Pack 2 for Windows XP, as well as Service Pack 1 for Windows Server 2003, were installed by users more quickly than it otherwise might have been. While the Windows 9x series offered the option of having profiles for multiple users, they had no concept of access privileges, and did not allow concurrent access; and so were not true multi-user operating systems. In addition, they implemented only partial memory protection. They were accordingly widely criticised for lack of security. The Windows NT series of operating systems, by contrast, are true multi-user, and implement absolute memory protection. However, a lot of the advantages of being a true multi-user operating system were nullified by the fact that, prior to Windows Vista, the first user account created during the setup process was an administrator account, which was also the default for new accounts. Though Windows XP did have limited accounts, the majority of home users did not change to an account type with fewer rights – partially due to the number of programs which unnecessarily required administrator rights – and so most home users ran as administrator all the time. Windows Vista changes this by introducing a privilege elevation system called User Account Control. When logging in as a standard user, a logon session is created and a token containing only the most basic privileges is assigned. In this way, the new logon session is incapable of making changes that would affect the entire system. When logging in as a user in the Administrators group, two separate tokens are assigned. The first token contains all privileges typically awarded to an administrator, and the second is a restricted token similar to what a standard user would receive. User applications, including the Windows shell, are then started with the restricted token, resulting in a reduced privilege environment even under an Administrator account. When an application requests higher privileges or "Run as administrator" is clicked, UAC will prompt for confirmation and, if consent is given (including administrator credentials if the account requesting the elevation is not a member of the administrators group), start the process using the unrestricted token. Leaked documents published by WikiLeaks, codenamed Vault 7 and dated from 2013 to 2016, detail the capabilities of the CIA to perform electronic surveillance and cyber warfare, such as the ability to compromise operating systems such as Microsoft Windows. In August 2019, computer experts reported that the BlueKeep security vulnerability, , that potentially affects older unpatched Microsoft Windows versions via the program's Remote Desktop Protocol, allowing for the possibility of remote code execution, may now include related flaws, collectively named DejaBlue, affecting newer Windows versions (i.e., Windows 7 and all recent versions) as well. In addition, experts reported a Microsoft security vulnerability, , based on legacy code involving Microsoft CTF and ctfmon (ctfmon.exe), that affects all Windows versions from the older Windows XP version to the most recent Windows 10 versions; a patch to correct the flaw is currently available. File permissions All Windows versions from Windows NT 3 have been based on a file system permission system referred to as AGDLP (Accounts, Global, Domain Local, Permissions) in which file permissions are applied to the file/folder in the form of a 'local group' which then has other 'global groups' as members. These global groups then hold other groups or users depending on different Windows versions used. This system varies from other vendor products such as Linux and NetWare due to the 'static' allocation of permission being applied directly to the file or folder. However using this process of AGLP/AGDLP/AGUDLP allows a small number of static permissions to be applied and allows for easy changes to the account groups without reapplying the file permissions on the files and folders. Alternative implementations Owing to the operating system's popularity, a number of applications have been released that aim to provide compatibility with Windows applications, either as a compatibility layer for another operating system, or as a standalone system that can run software written for Windows out of the box. These include: Wine – a free and open-source implementation of the Windows API, allowing one to run many Windows applications on x86-based platforms, including UNIX, Linux and macOS. Wine developers refer to it as a "compatibility layer" and use Windows-style APIs to emulate Windows environment. CrossOver – a Wine package with licensed fonts. Its developers are regular contributors to Wine, and focus on Wine running officially supported applications. Cedega – a proprietary fork of Wine by TransGaming Technologies, designed specifically for running Microsoft Windows games on Linux. A version of Cedega known as Cider allows Windows games to run on macOS. Since Wine was licensed under the LGPL, Cedega has been unable to port the improvements made to Wine to their proprietary codebase. Cedega ceased its service in February 2011. Darwine – a port of Wine for macOS and Darwin. Operates by running Wine on QEMU. Linux Unified Kernel – a set of patches to the Linux kernel allowing many Windows executable files in Linux (using Wine DLLs); and some Windows drivers to be used. ReactOS – an open-source OS intended to run the same software as Windows, originally designed to simulate Windows NT 4.0, now aiming at Windows 7 compatibility. It has been in the development stage since 1996. Linspire – formerly LindowsOS, a commercial Linux distribution initially created with the goal of running major Windows software. Changed its name to Linspire after Microsoft v. Lindows. Discontinued in favor of Xandros Desktop, that was also later discontinued. Freedows OS – an open-source attempt at creating a Windows clone for x86 platforms, intended to be released under the GNU General Public License. Started in 1996, by Reece K. Sellin, the project was never completed, getting only to the stage of design discussions which featured a number of novel concepts until it was suspended in 2002. See also Architecture of Windows NT Azure Sphere, Microsoft's Linux-based operating system BlueKeep De facto standard Dominant design Windows Subsystem for Linux, a subsystem in Windows 10, not using the Linux kernel; reimplementing Wintel References External links Official Windows Blog Microsoft Developer Network Windows Developer Center Microsoft Windows History Timeline Pearson Education, InformIT – History of Microsoft Windows Microsoft Business Software Solutions Windows 10 release Information 1985 software Computer-related introductions in 1985 Computing platforms Microsoft franchises Personal computers Windows Operating system families Products introduced in 1985	Operating System (OS)	4
Glossary of operating systems terms This page is a glossary of Operating systems terminology. A access token: In Microsoft Windows operating systems, an access token contains the security credentials for a login session and identifies the user, the user's groups, the user's privileges, and, in some cases, a particular application. B binary semaphore: See semaphore. booting: In computing, booting (also known as booting up) is the initial set of operations that a computer performs after electrical power is switched on or when the computer is reset. This can take tens of seconds and typically involves performing a power-on self-test, locating and initializing peripheral devices, and then finding, loading and starting the operating system. C cache: In computer science, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere. cloud: Cloud computing operating systems are recent, and were not mentioned in Gagne's 8th Edition (2009). In contrast, by Gagne's 9th (2012), cloud o/s received 3 pages of coverage (41, 42, 716). Doeppner (2011) mentions them (p. 3), but only to prove that operating systems "are not a solved problem" and that even if the day of the dedicated PC is waning, cloud computing has created an entirely new opportunity for o/s development ala sharing, networks, memory, parallelism, etc. Gagne (2012) adds that in addition to numerous traditional o/s's at cloud warehouses, Virtual machine o/s (VMMs), Eucalyptus, Vware, vCloud Director and others are being developed specifically for cloud management with numerous traditional o/s features (security, threads, file and memory management, guis, etc.) (p. 42). Microsoft's investment in cloud aspects of o/s tend to support that argument. concurrency D daemon: Operating systems often start daemons at boot time and serve the function of responding to network requests, hardware activity, or other programs by performing some task. Daemons can also configure hardware (like udevd on some Linux systems), run scheduled tasks (like cron), and perform a variety of other tasks. E F G H I J K kernel: In computing, the kernel is a computer program that manages input/output requests from software and translates them into data processing instructions for the central processing unit and other electronic components of a computer. The kernel is a fundamental part of a modern computer's operating system. L lock: In computer science, a lock or mutex (from mutual exclusion) is a synchronization mechanism for enforcing limits on access to a resource in an environment where there are many threads of execution. A lock is designed to enforce a mutual exclusion concurrency control policy. M mutual exclusion: Mutual exclusion is to allow only one process at a time to access the same critical section (a part of code which accesses the critical resource). This helps prevent race conditions. mutex: See lock. N O P paging daemon: See daemon. process Q R S semaphore: In computer science, particularly in operating systems, a semaphore is a variable or abstract data type that is used for controlling access, by multiple processes, to a common resource in a parallel programming or a multi user environment. T thread: In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by an operating system scheduler. The scheduler itself is a light-weight process. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. templating: In an o/s context, templating refers to creating a single virtual machine image as a guest operating system, then saving it as a tool for multiple running virtual machines (Gagne, 2012, p. 716). The technique is used both in virtualization and cloud computing management, and is common in large server warehouses. U V W Z References External links IBM's Glossary of Z/OS terms at IBM.com Operating Systems Glossary at Whatis.com Itanium architecture specification at Intel.com Linux Journalling Flash File System (JFFS) at Sourceware.org See also List of technology terms Comparison of operating systems List of important publications in operating systems List of operating systems Timeline of operating systems Operating systems Lists of computer terms	Operating System (OS)	5
OS/8 OS/8 was the primary operating system used on the Digital Equipment Corporation's PDP-8 minicomputer. Pre-OS/8 there were earlier PDP-8 operating systems: R-L Monitor, also referred to as MS/8. P?S/8, requiring only 4K of memory. PDP-8 4K Disk Monitor System PS/8 ("Programming System/8"), requiring 8K. This is what became OS/8 in 1971. Other/related DEC operating systems were: OS/78, OS/278, OS/12. The latter is a virtually identical version of OS/8, and was used with Digital's PDP-12 computer. Digital released OS/8 images for non-commercial purposes which can be emulated through SIMH. Overview OS/8 provided a simple operating environment that was commensurate in complexity and scale with the PDP-8 computers on which it ran. I/O was supported via a series of supplied drivers which used polled (not interrupt-driven) techniques. The device drivers had to be cleverly written as they could occupy only one or two memory pages of 128 12-bit words, and had to be able to run in any page in field 0. This often required considerable cleverness, such as the use of the OPR instruction (7XXX) for small negative constants. The memory-resident "footprint" of OS/8 was only 256 words; 128 words at the top of Field 0 and 128 words at the top of Field 1. The rest of the operating system (the USR, "User Service Routines") was swapped in and out of memory transparently (with regard to the user's program) as needed. The Concise Command Language Early versions of OS/8 had a very rudimentary command-line interpreter with very few basic commands: GET, SAVE, RUN, ASSIGN, DEASSIGN, and ODT. With version 3 they added a more sophisticated overlay called CCL (Concise Command Language) that implemented many more commands. OS/8's CCL was directly patterned after the CCL found on Digital's PDP-10 systems running TOPS-10. In fact, much of the OS/8 software system was deliberately designed to mimic, as closely as possible, the TOPS-10 operating environment. (The CCL command language was later used on PDP-11 computers running RT-11, RSX-11, and RSTS/E, providing a similar user operating environment across all three architectures: PDP-8s, PDP-10s, and PDP-11s.) The basic OS and CCL implemented many rather sophisticated commands, many of which still do not exist in modern command languages, not even in MS-DOS, Windows, or Unix-like operating systems. For example, the COMPILE command would automatically find the right compiler for a given source file and start the compile/assemble/link cycle. The ASSIGN and DEASSIGN commands allowed one to use logical device names in a program instead of physical names (as required in MS-DOS). For example, your program could write to device FLOP:AAA.TXT, and if you first did an "ASSIGN FLOP: RXA2:" then the file would be created on physical device RXA2 (the second floppy disk drive). VAX/VMS and the Commodore Amiga's operating system AmigaOS (and other OSes built around Tripos) made considerable use of this very flexible feature. The SET command was capable of setting many system options, albeit by the crude method of patching locations in the system binary code. One of them, a command under OS-78, was SET SYS OS8, and it re-enabled the MONITOR commands that were not part of OS-78. The BUILD command could reconfigure the OS on the fly, even adding device drivers, often without having to reboot the OS. The OS can boot from a hard disk and present the command prompt in under half a second. The OS/8 Filesystem OS/8 supported a simple, flat file system on a variety of mass storage devices including: TU56 DECtapes DF32 32KW fixed-head disks RF08 256KW fixed-head disks RK01/02/03/04/05 cartridge disk drives RL01/02 cartridge disk drives RX01/02 floppy diskette drives Filenames on the PDP-8 took the form of FFFFFF.XX where "F" represents an uppercase, alphanumeric character of the filename and "X" represents an upper-case, alphanumeric character of the extension (filetype). .PA : Assembly language .SV : saved core-images (executable programs) .FT : Fortran source files .DA : Data files The contents of any given file was stored contiguously in a single "extent". PIP included an option to compress ("squeeze") the filesystem, so that all unallocated space was moved to a single extent at the end of the disk. This could be invoked by the SQuish CCL command, much as MUNG could be used to run a TECO macro. OS/8 volumes had a very limited maximum storage size (4096 blocks of 256 12-bit words) and the RK05 (2.4MB) moving-head disk exceeded this size: "1.6 million words of storage." Because of this, RK05 cartridges were divided into two partitions. For example, the first RK05 on a system would be known as both RKA0: (SY:) and RKB0:. This division was commonly thought to mean "the upper surface" and "the lower surface" but this was incorrect; it in fact was "the outer cylinders" and "the inner cylinders". ASCII files ASCII files were stored as 3 8-bit characters per pair of 12-bit words: Characters 1 & 2 on the right of words 1 & 2, with bits 0-3 & 4-7 of the 3rd character stored in the leftmost bits of the pair of words. WORD 1: c0 c1 c2 c3 \| a0 a1 a2 a3 a4 a5 a6 a7 WORD 2: c4 c5 c6 c7 \| b0 b1 b2 b3 b4 b5 b6 b7ASCII files end with a CTRL/Z (ASCII 232). OS/8 date format OS/8 allocated the PDP-8's 12 bit words for storing dates per: 4 bits for the month 5 bits for the date therein 3 bits for the year. Y3B! This was recognized when COS-310 was developed. OS/8 CUSPs (Utility Programs) The CUSPs (Commonly-Used System Programs, that is utilities) supplied with OS/8 included: BUILD (the program to install a configured OS/8 system onto mass storage) DIR (the directory-listing program) EDIT (A line-oriented editor) MACREL (A relocating assembler that, unlike PAL, implemented macros. Written by Stanley Rabinowitz of DEC's Small Systems Group. Stan had an ASCII-artwork picture of a fish in his office that said "MACREL IS A FISH") FLAP (An absolute assembler derived from RALF) FORTRAN-II. FOTP (File-Oriented Transfer Program, an alternative to PIP) PAL (The assembler) PIP (the Peripheral Interchange Program, used to copy files) PIP10 (a version of PIP used to copy files to from PDP-10 DECtapes) RALF (Another relocating assembler for the FPP) TECO (Text Editor and COrrector, a much-more-sophisticated editor). The MUNG command ran TECO macros. CCL, the command line interpreter, was supplied in source form and could be extended by the user. Programming languages BASIC A single-user BASIC and two multi-user versions of BASIC were available as options. The single-user BASIC used several overlays to provide the full functionality of the language; when OS/8 was booted from a DECtape, a very noticeable delay occurred each time BASIC was required to switch overlays as they needed to be read from tape. The multi-user versions of BASIC (EDU20 and EDU25) differed only in whether or not they supported block-replaceable devices (DECtape or disk). Due to cost constraints, many PDP-8s had punched paper tape readers as their only mass-storage I/O device. EDU20 loaded from paper tape and could do output to a paper tape writer if the machine had one, whereas EDU25 understood the structure of a filesystem, could load from DECtape or disk, and could create files on DECtape or disk. Both could run multiple BASIC programs simultaneously using a primitive task-scheduler that round-robined among the attached terminals. Memory was always very tight because the PDP-8 used core memory, which was extremely expensive compared to RAM technology which came along a few years later. In a mere 8K of 12-bit words EDU20 could support up to 4 terminals at once, although more memory was recommended. EDU25 required an additional 4K memory bank (for a minimum of 12K) because the code contained a disk device driver and a filesystem handler. While running, EDU20 and EDU25 were self-contained programs that didn't use any OS/8 system calls. Immediately upon being invoked from the OS/8 command interpreter they would overwrite OS/8's entire resident portion - all 256 words of it. Upon startup, EDU25 would save the contents of memory to DECtape or disk and restore it when it exited. But EDU20 could not do this as it was targeted at hardware configurations without any block-replaceable device. FORTRAN In addition to a freely available FORTRAN II compiler, there was also a rather complete FORTRAN IV compiler available at extra cost. This compiler generated code for the optional FPP-8 floating-point processor, which was essentially a separate CPU, only sharing memory with the PDP-8 CPU. If you had the FPP-8 option installed, the FORTRAN runtime code would detect it and use the FPP-8 to run the main program code, and the PDP-8 CPU would run as an I/O processor. If you did not have the FPP-8, the runtime code would instead call an FPP-8 interpreter running on the PDP-8 CPU, so the program would still run, but at considerably reduced speed. This FORTRAN IV compiler in version 1 had the interesting bug that DO loops counted incorrectly: DO loops would count 1,2,3,5,6,7,… (skipping 4). A quick patch was released to fix this. See also Multics Unix TSS-8 References External links SIMH Software Kits including an OS/8 image. OS/8 Manuals at Bitsavers. Links to DEC's Hobbyist License & documentation DEC operating systems 1971 software	Operating System (OS)	6
"Comparison of operating systems\nThese tables provide a comparison of operating systems, of compute(...TRUNCATED)	Operating System (OS)	7
"History of operating systems\nComputer operating systems (OSes) provide a set of functions needed a(...TRUNCATED)	Operating System (OS)	8
"OS/360 and successors\nOS/360, officially known as IBM System/360 Operating System, is a discontinu(...TRUNCATED)	Operating System (OS)	9

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