# Computer Hardware

NOTE:- This book is currently in the process of being merged. Some data could be out of place or already merged. Personal Computers (PCs) can be obtained in desktop, laptop, notebook and other portable formats.
They are used in all areas of society.
This module describes the parts of typical desktop personal computers.
please add your contributions
Note: Should this stuff be moved to other pages?
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# Computer hardware

* The Motherboard and things directly attached to it.
* Computer chassis and screen, preferly with standard sizes (i.e. ISO A4 for notebook chassis).
* Storage media
* Other peripherals

# Class 1 Components

Class 1 components are integral to the function of the computer.

## CPU

The CPU (Central Processing Unit) is the 'brain' of the computer.
It's typically a square ceramic package plugged into the motherboard, with a large heat sink on top (and often a fan on top of that heat sink).
All instructions to the computer are processed by the CPU. There are many "CPU architectures", each of which has its own characteristics and trade-offs. The dominant CPU architectures used in personal computing are x86 and ARM. x86 is easily the most popular processor for this class of machine (the dominant manufacturers of x86 CPUs are Intel and AMD). X64 is currently replacing X86 as it has superior performance. X86 is 32 bit, which means it has 6 0s and 1s to use at one instance while X64 can use 7 0s and 1s. Some programs are offered in 64-bit only.
The other architectures are used, for instance, in workstations, servers or embedded systems.
CPUs contain a small amount of static RAM (SRAM) called a cache. Some processors have two or three levels of cache, containing as much as several megabytes of memory.
Dual Core
Some of the new processors made by Intel and AMD are Dual core. The Intel designation for dual core are "Pentium D", "Core Duo" and "Core 2 Duo" while AMD has its "X2" series and "FX-6x".
The core is where the data is processed and turned into commands directed at the rest of the computer. Having two cores increases the data flow into the processor and the command flow out of the processor potentially doubling the processing power, but the increased performance is only visible with multithreaded applications and heavy multitasking.
Hyper Threading
Hyper Threading is a technology that uses one core but adds a virtual processor to an additional thread at the same time.
Normally the processor carries out one task and then proceeds onto the next task. But with Hyper Threading the processor continually switches in-between each task as if to do them at the same time.
For more information, consult the Wikipedia article on microprocessors.

## Case

Most modern computers have an "ATX form factor" case in which ATX-compatible power supplies, Mainboards and Drives can be mounted.
During the 1980s and 1990s almost all cases were beige, even Apple's Macintosh line. A few rare exceptions to this were black. Only recently have computer case designers realized that there was a worthwhile market for other colors and designs. This has led to all sorts of modifications to the basic design of a computer case. Now it is easy to find cases with transparent windows and glowing lights illuminating their insides.

## Power Supply

All computers have some sort of power supply. This converts the supply voltage (AC 110 or 220 V) to different voltages such as DC 5 V, 12 V and 3.3 V. These are needed inside the computer system by nearly every component inside the computer.
There will be a bunch of connectors coming off of the supply, called Molex connectors. They come in varying sizes, meant for different applications, such as the motherboard (usually the largest of the connectors), the hard and optical drives (a bunch of medium-sized connectors), as well as the floppy drive (a relatively small connector, also saw usage among videocards in 2004). As newer standards come out, the types of connectors have changed. Many power supplies now come with power connectors for Serial ATA hard drives. These are smaller and are "hot-swappable", meaning they can be removed and plugged in again without fear of data loss or electrical problems.

## Motherboard

The Motherboard (also called Mainboard) is a large, thin, flat, rectangular fiberglass board (typically green in the past but are now typically black due to consumer demands) attached to the case. The Motherboard carries the CPU, the RAM, the chipset and the expansion slots (PCI, AGP - for graphics -, ISA, etc.).
The Motherboard also holds things like the BIOS (Basic Input Output System) and the CMOS Battery (a coin cell that keeps an embbeded RAM in the motherboard -often NVRAM- powered to keep various settings in effect).
Most modern motherboards have onboard sound and LAN controller, some of them even have on-board graphics. These are adequate for standard office work and system sounds. But dedicated sound and graphics cards plugged into the expansion slots offer much better quality and performance

## RAM

Random Access Memory (RAM) is a memory that the microprocessor uses to store data during processing. This memory is volatile (loses its contents at power-down). When a software application is launched, the executable program is loaded from hard drive to the RAM. The microprocessor supplies address into the RAM to read instructions and data from it. RAM is needed because hard drives are too slow to operate with the speed of a microprocessor.
Some of the types of RAM are SDRAM, SRAM, DDR RAM, Rambus RAM, SIMM, DIMM.

### External links

* http://themonitormonitor.com/ultimate-guide-computer-memory/ (Ultimate Guide To Memory)

## PCI Express Cards/Slots

The PCI Express standard was created to replace both AGP and PCI slots, with PCI Express 16x and PCI 1x respectively for most implementations. The current implementation of PCI Express allows up to PCI Express 32x.
The reason for the change is that the older PCI cards don't transfer data quickly enough to keep up with modern day gaming, Autocad and video editing software.
Think of it this way, there is a tap that is two inches in diameter, but a drain that is only one inch in diameter. The water doesn't drain quickly enough and eventually the sink overflows. Just like a PCI video card.

## AGP Cards

Most graphic cards produced from about 1998-2004 were AGP (Accelerated Graphics Port) cards. They are placed in a certain slot on the mainboard with an extra high data transfer rate. The interface was invented to keep the graphics card away from the PCI bus, which was starting to become too constrained for modern graphics cards.
Every graphic card carries a graphic chip (GPU) and very fast DDR RAM for textures and 3D data. Their data buses have 1X, 2X, 4X, and 8X speeds. The bus is 32-bit, much like PCI.
AGP slots are slightly shorter than PCI slots and often brown in color. A similar type of slot called AGP Pro is longer and has extra power leads to accommodate modern video cards. It didn't really catch on in the mainstream market, and graphics card makers preferred to add an extra power connector to supply the power they needed.

## PCI Cards

The PCI (Peripheral Component Interconnect) bus is the most popular internal interconnect for personal computers. They are usually white in color.
The specification features:
* Plug and play configuration (through standardised means for interacting with configuration software)
* Standardised electrical connections
Common PCI implementations in desktop PCs feature:
* 32-bit addressing
* 33-MHz bus clock
High-end implementations may also feature:
* 64-bit addressing
* "Hot plugging" (the ability to add / remove PCI devices from a running machine)
* 66-MHz bus clock
(all of these are characteristic of PCI-X)
There have been many revisions and evolutions of the PCI specification over the years. Recently, PCI-X has sought to extend the aging architecture for the needs of modern server-class machines, avoiding some of the performance bottlenecks of previous revisions. The new PCI Express specification seems likely to succeed PCI in all classes of personal computer within the next few years.

## ISA Cards

Industry Standard Architecture (ISA) cards were the original PC extension cards. Originally running on an 8-bit bus, they ran on a 16-bit bus as of 1984. Like PCI slots, they supported Plug-and-Play as of 1993 (prior to this, one had to set jumpers for IRQ interrupts and such). In comparison to PCI slots, they are rather long, and often black in color. They are not found on most computers built after 1999.

## Other removable media
### Flash memory

Some common types of Flash memory cards are CompactFlash, Secure Digital (SD), and xD. There are other formats which are falling into disuse, such as Smartmedia (SM) and MultiMediaCard (MMC).
Flash memory is faster than magnetic media and much more rugged. The main reason Flash hasn't yet replaced hard drives is that Flash memory is much more expensive per gigabyte than hard drives.

### USB Flash drive

Not everyone is familiar with exactly what a USB Flash Drive is, what it’s used for and why they are becoming increasing popular. So here’s a basic guide to what a USB Flash Drive is:
USB Flash drives (also known as USB memory sticks, USB pen drives or USB thumb drives) were first commercially available in the year 2000. IBM launched them under the brand name “DiskOnKey” and they were introduced as a replacement for the floppy disc. By today’s standard the first USB flash drives had a tiny 8MB of storage capacity but even this was 4 times the amount of data that could be stored on a floppy disk.
The portability of USB flash drives and the ability to carry your data around on a key ring or lanyard and simply plug it into a PC via a USB port meant they became very popular very quickly. Essentially a USB flash drive is a just a way of storing data and storing it on something that is lightweight, easy to carry, easy to use and works on all PC and Mac platforms.
Over time larger storage capacities became available and the data transfer speeds increased to support the movement of larger amounts of information. Today typical USB flash drives are 2GB to 4GB but drives up to a whopping 64GB are now making their way into the market. A 64GB flash drive holds 8,000 times more data than the 8MB version first introduced in 2000!!
Inside every USB flash drive is a small printed circuit board (controller chip) that is connected to a flash memory module (the piece on which the data is stored). These two elements are then encased in an outer shell that is typically made of plastic, metal or more recently wood/bamboo.
The USB connector that protrudes out of the end of a flash drive is simply inserted into any PC or Mac and then the storage space on the USB flash drive is accessible and data can to saved to/from the drive. USB flash drives don’t need batteries because they draw all the power they need to work from the USB port they are plugged into.
Today USB flash drives are very popular with companies because they can print their logo or brand onto the outside casing of the flash drive and give them away at trade shows, conferenceHealth Fitness Articles, exhibitions and so on. With the large amount of storage space now available on entry level versions of the flash drive companies are also pre-loading their sales brochures and other marketing material onto the memory of the flash drive – this not only saves them printing and transportation costs but it’s a really effective way of distributing large amounts of data and information about their company.
People that are given branded flash drives (flash drives printed with a company logo on) are typically delighted to receive them because they have a high perceived value and because they can use they to save and transport their own data around.

# Class 3 Components: Peripherals

Class 3 components are components which allow humans to interface with computers.

## Display device

Includes computer monitors and other display devices. CRTs and LCDs are common. LCDs are a more recent development, and are gradually replacing CRTs as they become more affordable. LCDs in addition to being lighter also use less energy and generate less heat.

## Sound Output

Includes internal or external speakers and headphones.

## Mouse

A user interface device that can enable different kinds of control than a keyboard, particularly in GUIs. It was developed at the Xerox PARC (Palo Alto Research Center) and adopted and made popular with the Apple Mac. Today, nearly all modern operating systems can use a mouse. Most mice (sometimes the plural is 'mouses' to prevent confusion with the rodent) are made from plastic, and may use a ball to track movement, an LED light, or a laser. Today you can get a wireless mouse that allows you to easily give a presentation without being tied to a desk. These mouses are usually LED or Laser based tracking.

### History

In 1964, the first prototype computer mouse was made to use with a graphical user interface (GUI), windows. Douglas Engelbart received a patent for the wooden shell with two metal wheels (computer mouse U.S. Patent # 3,541,541) in 1970, describing it in the patent application as an "X-Y position indicator for a display system.". It was nicknamed the mouse because the tail came out the end, Engelbart revealed about his invention. His version of windows was not considered patentable (no software patents were issued at that time), but Douglas Engelbart has over 45 other patents to his name. There was also a DB-9 connector that was used to be an old serial mouse connector.

## Keyboard

A keyboard is an input device which is connected to a computer and used to type instructions or information into the computer. Typically, a keyboard has about 100 or so keys.
* Keyboards differ between languages. Most English-speaking people use what is called a QWERTY layout. This refers to the order of the top row of keys. Some foreign languages (i. e. German) use QWERTZ, where the Z and Y are switched.
* Many laptop computers do not include a number pad. (There is sometimes a function on the keyboard to enable a numpad-like mode.)
* Modern keyboards sometimes have extra controls such as volume, and keys that can be programmed to bring up programs of the user's choice.

## Printer

A printer makes marks on paper. It can print images and text.
The most common types of printers today are
* Laser printer: Prints very crisp text, but cheaper models can only print in black and white. Good for places like offices where high printing speed is needed.
* Color inkjet printer: Prints photos and other images in color (using 4 colors of ink—cyan, magenta, yellow, and black), but the text they print is often not as crisp as a laser printer.
The average printer of the early 1990s would connect to a computer through its parallel port. To connect it to the computer via parallel port, one would have to screw it into the port. Today many printers are connected through USB. This is because it is easier to connect and remove through a simple plug and play system. It also allows for faster transfer speeds than parallel.

## Scanner

A scanner is a device for digitizing paper documents into images that may be manipulated by a computer. The two main classes of scanner are
* hand-held scanners (in which the user manually drags a small scanning head over the document), and
* flat-bed scanners (which are designed to accommodate a whole sheet of paper, which is then examined by a motorised scanning head).
If the original document contained text, Optical Character Recognition (OCR) software may be used to reconstruct the text of the document from the scanned images.

## Modem

A contraction of "Modulator - demodulator", a modem allows a computer to communicate over an analogue medium (most commonly a telephone line). The modem encodes digital signals from the computer as analogue signals suitable for transmission (modulation) and decodes digital data from a modulated analogue signal (demodulation). Using modems two computers may communicate over a telephone line, with the data passed between them being represented as sound.
Modems are usually involved with dial-up internet services. As broadband catches on, they are falling into disuse. However, the devices used to connect to broadband connections are also called modems, specifically DSL Modems or Cable Modems.

## CD-Roms

A CDROM (compact disk read-only memory), also written as CD-ROM, is a type of optical storage media that allows data to be written to it only once. This contrasts with memory, whose contents can be accessed (i.e., read and written to) at extremely high speeds but which are retained only temporarily (i.e., while in use or only as long as the power supply remains on). Although the disc media and the drives of the CD and CD-ROM are, in principle, the same, there is a difference in the way data storage is organized. Two new sectors were defined, Mode 1 for storing computer data and Mode 2 for compressed audio or video/graphic data.

### CD-ROM Mode 1

It is the mode used for CD-ROMs that carry data and applications only. In order to access the thousands of data files that may be present on this type of CD, precise addressing is necessary

### CD-ROM Mode 2

CD-ROM Mode 2 is used for compressed audio/video information and uses only two layers of error detection and correction, the same as the CD-DA. Therefore, all 2,336 bytes of data behind the sync and header bytes are for user data

# Appendix A: Connectors and Cables

There are many different types of connectors and cables in personal computers, and this section will address as many as the various editors deem relevant.

## Internal Connectors

Several types of cables are used to connect components together inside the case, providing power and a path for data. These include:
* Motherboard Power Connector: This connector is designed especially to move electricity from the power supply to the motherboard. Older computers use the AT power connections, with two six-pin connectors lined up side by side. ATX motherboards used a single connector with 20 pins arranged in two rows of 10.
** Many motherboards now also use supplementary power connectors, such as a 4 pin plug specifically for the CPU supply.
** Some others have more than 20 pins for the main connector. The extra pins are in the form of a 'separate' connector, that fits onto the end of the standard 20 pin connector. This may be used or not as required by the particular motherboard.
** The PCI-e interface may also require the use of further power cables from the power supply.
* Power Connectors for Drives: Hard drives, optical drives, and, increasingly, high-end video cards use a 4-wire power connection, of which several are available from a power supply. Floppy drives use a smaller connector.
** With the introduction of the SATA interface for data another type of power connector for drives was also introduced. This is thinner than the previous power connector.
* 40 and 80-pin IDE Cables: These cables are used by hard drives and optical drives to transfer data to and from the motherboard. These are now sometimes called PATA (Parallel ATA) cables to differentiate from the more recent SATA.
* SATA (Serial ATA) Cables: These cables are now used by most hard drives and even optical drives to carry data to and from the motherboard. They are much thinner than PATA ribbon cables, and the connectors are much smaller. Generally red coloured.
** SATA drives generally also require a new type of power connector, though some can also use the older white 'Molex' plug. Adaptors are available if the power supply doesn't have the correct connector.
* 34-pin Floppy Cables: These are used to connect floppy drives to floppy disk connectors on the mainboard/motherboard.

## External Connectors

Without connections to the rest of the world, a computer would just be a fancy paperweight. Numerous connectors are used to make a computer useful.
* AT Keyboard Connector: Found on older computers, this connector is large and round with five pins.
* PS/2 Connector: This connector is currently the most popular for connecting both the keyboard and mouse. Note that older mice once used serial ports (defined below), and newer mice frequently use the Universal Serial Bus (USB).
* VGA Connector: This connector has 3 rows of 5 pins each, and is used to connect the computer to the display screen.
* Parallel Port (DB-25): This connector is commonly used to interface with printers, and can also transfer between computers. It has been mostly replaced by USB.
* Serial Port (DB-9): This 9-pin connector is used to connect all sorts of devices, but is being replaced by USB. It has been used in the past to connect mice and transfer data between computers.
* Universal Serial Bus (USB): This relatively recent connector can connect the computer to almost anything. It has been used for storage devices, printers, sound, mice, keyboards, cameras, and even networking. USB 2.0 allows transfer speeds of up to 480 Mbit/s.
* FireWire (IEEE 1394) port: This high-speed connection runs at 400 Mbit/s (1394a) or 800 Mbit/s (1394b), and can connect up to 63 external devices to a single port. Most digital camcorders have a firewire port to connect to a computer.
* RJ-11 (phone) Connectors: This is the type of connector you will see on phones and modems. It is not used for much else.
* RJ-45 Connectors: These are used to connect computers to an Ethernet network. Maximum speed of such a connection is now 1000 Mbit/s (= 1 Gbit/s).
* Audio Connectors: Three of these connectors can be found on an average sound card, and are used to connect to microphones (usually pink), speakers (usually green), and other audio devices (usually blue). The external device connector is usually a silver-colored or gold-plated plug that fits into a round hole.

# Units of Information

In the world of computers, a unit of information is how much a certain data storing system can hold and is used to measure how much other systems can hold as well. There are two types of units that are the most typical which are bits, which exist is two states, or bytes, the equivalent of eight bits. Bits make up the foundation of unit information. Without bits there would be no bytes, nibbles, nor words.
* Bytes or octets are the equivalent to eight bits.
* Nibbles are four bits or sometimes called half a byte.
* Words are most commonly known for having 16 bits but others in the past have used words with many different bits.