# History of Computers/The Operating System History
## Mainframe Operating Systems

* IBM BOS
* IBM TOS
* IBM DOS
* IBM OS/PCP
* IBM OS/MFT
* IBM OS/MVT
* IBM OS/VS1
* IBM OS/VS2
* IBM MVS
* IBM TSS Time-Sharing System
* IBM TSO Time-Sharing Option for OS/360
* (IBM) CP-67 Control Program/67
* (IBM)CMS Cambridge Monitor System
* IBM VM/370 Virtual Machine
* IBM VM/SP
* IBM VM/HPO
* IBM VM/ESA
* IBM VM/CMS Virtual Machine/Conversational Monitor System
* ICL GEORGE
* MTS Michigan Time-Sharing System
* IBM DOS/360 Disk Operating System 360
* IBM DOS/VS Disk Operating System/Virtual Storage
* IBM DOS/VSE Disk Operating System/Virtual Storage Extended
* IBM VSE/SP Virtual Storage Extended/System Package
* IBM SSX/VSE Small System Executive/Virtual Storage Extended
* IBM VSE/ESA Virtual Storage Extended/Enterprise Systems Architecture
* IBM z/VSE zSeries/Virtual Storage Extended
* Amdahl UTS Unix system
NB: Be more useful if added years of releases.

## Personal Computer Operating Systems

* QDOS
* CP/M
* MS-DOS

## Operating system 'wars'
### DOS & CP/M

When the PC was introduced, it needed an operating system. IBM approached a company named Digital Research, which was owned by Gary Kildall. IBM sought the use of Digital Research's CP/M, a popular operating system in earlier systems. (It was, in fact, the first operating system that wasn't hardware-specific.) IBM did not want to pay royalties, however, but sought a one time purchase, which included a rename. Digital Research refused, and IBM withdrew. They then approached Microsoft and Bill Gates, who purchased an existing operating system (Seattle Computer Company's 86-DOS) and renamed it MS-DOS. This name was later used on non-IBM models; Microsoft agreed to IBM's desire to use their own name, and the operating system was sold as PC-DOS on the PC.
86-DOS was modelled after CP/M, and Digital Research filed legal action for patent infringement. IBM settled by offering computer buyers a choice of either; however, CP/M-86 (as the PC version was named) cost almost $200 more than PC-DOS, and it did not sell well.
MS/PC-DOS quickly became the standard for the PC-compatible market. Digital Research would attempt to regain the market, eventually settling on an MS-DOS clone, DR-DOS. DR DOS was sold off the shelf (while MS/PC-DOS was only sold bundled with new computers), and would later gain a large market share with version 5, which had new memory management that broke down an early limitation of DOS, a maximum usable memory of 640 kB.

### Windows & Competition

By this time, Microsoft was holding the market not only with MS-DOS, but Microsoft Windows, a graphical shell program for DOS. Windows was based on the Macintosh, and Apple filed suit. Complicating the matter was a suit against Apple by Xerox, claiming that Xerox was the rightful owner of the design. Eventually, it was ruled that the design factors in question could not be copyrighted, and Macintosh and Windows continued to coexist.
In 1995, Windows was re-worked to be a self contained operating system, Windows 95. By this time, DR-DOS had been sold twice, becoming Novell DOS 7, then Caldera DR-DOS 7. IBM had also split from Microsoft and was developing PC-DOS 6 separately. The new version of Windows that didn't coexist with DOS was ultimately the focus of an anti-trust lawsuit against Microsoft. Despite this, Microsoft was able to continue developing Windows.
Today, the market is dominated by the IBM PC-compatible computer, the majority of which run Microsoft Windows. Also present is an up-and-coming system, Linux, which is an open source system based on UNIX (an alternate PC-compatible system dating to the late 1970s; it was more complex and used for industrial, rather than home, use). On a separate platform, the Apple Macintosh also exists, running the newest Apple operating system, Mac OS X. Mac OS X is a combination of Mac OS 9 and the NextOS operating system that Steve Jobs second company Next Inc. created based on BSD Unix and the MACH kernel. Since it is based on Unix, Mac OS X is a much better operating system than previous Macintosh operating systems and helped save Apple from losing money as without it, it would not be able to compete against Linux, or modern Windows operating systems.
OS/2 was a joint project by IBM and Microsoft to create an Advanced DOS (ADOS was the code name, a replacement for MS-DOS that makes use of the 80286 and 80386 processors and breaks 8088/8086 limitations) OS/2 1.X was based on the MS-Windows GUI, but IBM and Microsoft broke off support of each other and IBM licensed the AmigaDOS/Workbench 1.3 code to create the Workplace GUI based on Workbench for OS/2 2.0 and stopped using the Windows 2.X shell and Commodore Amiga got the IBM REXX scripting language in exchange named AREXX (Amiga REXX) for AmigaDOS/Workbench 2.0 to have a scripting language. Microsoft took their OS/2 code and made Windows NT (codenamed MS-OS/2 3.0 but renamed Windows NT and NT stood for New technology) and Windows NT 3.1 Workstation and Server were invented by Microsoft. IBM improved OS/2 and named OS/2 3.0 as OS/2 Warp taking a Star Trek name and joked about "Arrive in Chicago earlier than expected" in that OS/2 Warp could do what Windows 95 code named Chicago could do but OS/2 Warp came out before Windows 95. Microsoft beat OS/2 Warp by using OEM agreements that each new PC would ship with Windows 95 and pay for a Windows 95 license even if the PC ran a different OS like OS/2 Warp, and shut IBM out of the PC market. IBM sold PS/2 and later VaulePoint and other systems like IBM Thinkpads with OS/2 Warp and then later OS/2 Merlin or OS/2 4.0. Eventually IBM gave up on OS/2 and migrated towards Linux, and licensed OS/2 to an OEM named Serenity Systems that made eComStation based on it, a more modern OS/2 based operating system. OS/2 was billed as "A better DOS than DOS, and a better Windows than Windows" because it ran MS-DOS programs in a Window, and used WIN-OS2 based on Windows 3.X to run 16 bit Windows programs. OS/2 also ran OS/2 command line and OS/2 GUI mode programs native as well. Some say OS/2's failure was that it ran DOS and Windows programs, so nobody wanted to make OS/2 native programs for it. Microsoft shut IBM out of the 32 bit Windows code and then OS/2 couldn't run Windows NT or Windows 95 software, until later when the ODIN project was based on the Linux WINE project to run some 32 bit Windows code. By that time it was too late and Microsoft Windows dominated OS/2.