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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.
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- 1 Computer hardware
- 2 Class 1 Components
- 3 Class 2 Components: Storage
- 4 Class 3 Components: Peripherals
- 5 Appendix A: Connectors and Cables
- 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.
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 the computer will process 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 PowerPC. x86 is easily the most popular processor for this class of machine (the dominant manufacturers of x86 CPUs are Intel and AMD). The other architectures are used, for istance, 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.
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 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.
Most modern computers have an "ATX form factor" case in which ATX-compatible power supplies, Mainboards and Drives can be mounted.
The Mini-ITX is much different in important ways unlike its relatives the Micro-ATX and the Flex-ATX. The mainboard size can be up to 170mm x 170 mm which is smaller than the Flex and Micro-ATX can be. Usually at less than 100 watts, the Mini-ITX PSU is energy efficient. The Mini-ITX is also backward-compatible with the Flex/Micro-ATX models.
During the 1980's and 1990's 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.
All computers have some sort of power supply. This converts the supply voltage (AC 110 or 220V) to different voltages such as DC 5V, 12V and 3.3V. 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.
The power supply also has an exhaust fan that is responsible for cooling the power supply, as well as providing a hot air exhaust for the entire case. Some power supplies have two fans to promote this effect.
It is important to buy a power supply that can accommodate all of the components involved. Some may argue that it is the most important part of a computer, and therefore it is worth spending the money to get a decent one.
The Motherboard (also called Mainboard) is a large, thin, flat, rectangular fiberglass board (typically green) 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
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.
- http://www.kingston.com/tools/umg/default.asp (Ultimate memory guide)
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.
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.
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.
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.
Class 2 Components: Storage
Class 2 components are storage media for non-volatile data.
Do not put magnetic media (including floppy disks, hard drives, video cassette tape) through airport X-ray machines. The X-rays themselves are not the problem -- it's the magnetic fields from the conveyor-belt motors that all too often erase magnetic media.
Optical media -- Compact Disks (CDs) and the similar-looking DVDs -- are completely immune to magnetic fields. They can be run through airport X-ray machines without any problems.
Flash memory is also immune to magnetic fields.
Sometimes one can distinguish between "fixed media" (the hard drive) that is more or less permanently mounted inside the computer case, and "removable media" (just about every other kind of media) that is easy to pull from one computer and put into another computer.
Floppy Disk drives
8" Floppy Disk: In the late 1960s IBM invented the 8-inch floppy disk. This was the first floppy disk design. Used in the 1970s and as a read-only disk it had storage-write restrictions to the people it was distributed to. However, later on a read-write format came about. In today's modern society it is rare to find a computer that uses the 8-inch floppy disk.
5.25" Floppy Disk: This disk was introduced some time later, and was used extensively in the 1980s.
3.5" Floppy Disk: This storage medium is the most common of those listed in this section, still in somewhat wide use today. Floppy disks hold from 400 KB up to 1.44 MB. The most common types found are 720 KB (low-density) and 1.44 MB (high-density). Floppy disks have largely been superseded as a transfer medium, first by rewritable CD-ROM (CD-RW) drives and now by flash drives, but are still used as backup storage for small amounts of data. A fair proportion also survive as original installation media for older software applications.
Several other floppy types and sizes have been introduced, such as 2", 2.5" and several competing 3" and 3.25" formats as well as the ~120 MB SuperDrive which was compatible with standard 3.5" disks, but none of these were ever very popular and all are quite rare now. Recently, it has become increasingly common for computers to be manufactured without floppy disk drives, and even some motherboards lack standard floppy disk connection headers, so it is expected that the floppy disk will soon fade completely from general use.
A hard drive consists of one or more magnetic platters or disks and a read arm with two electromagnetic coils for each disk. Each hard disk is divided into many sectors, each containing a certain amount of data. As of now, it is the cheapest and most common way to store a lot of data in a small space.
Compact Disc Read Only Memory (CD-ROM) is a standard format for storing a variety of data. A CD-ROM holds about 700 MB of data. The media resembles a small, somewhat flexible plastic disc. Any scratch or abrasion on the data side of the disc can lead to it being unreadable.
Cleaning CD's: Dust can be removed from a CD's surface using compressed air or by very lightly wiping the information side with a very soft cloth (such as an eyeglass cleaning cloth) from the center of the disc in an outward direction. Wiping the information surface of any type of CD in a circular motion around the center, however, has been known to create scratches in the same direction as the information and potentially cause data loss. Fingerprints or stubborn dust can be removed from the information surface by wiping it with a cloth dampened with diluted dish detergent (then rinsing) or alcohol (methylated spirits or isopropyl alcohol) and again wiping from the center outwards, with a very soft cloth (non-linting : polyester, nylon, etc.). It is harmful, however, to use acetone, nail polish remover, kerosene, petrol/gasoline, or any other type of petroleum-based solvent to clean a CD-R; the use of petroleum based solvents will damage the polycarbonate surface and the CD-R will become unreadable.
Compact disc Read/Write drives support the creation of CD-R and CD-RW discs, and also function as CD-ROM drives. These drives use low-powered lasers to 'burn' data into the active layer of the disc.
CD-R (Compact disc recordable) discs are 'write once' - once they have been written to, the data cannot be erased or changed. However, multisessions can be created and more data can be added.
CD-RW (Compact disc rewritable) discs can be rewritten or erased multiple times. This is a two-pass process so they typically take twice as long as CD-R discs to produce.
CD-RW drives will typically have three speed ratings - one for reading discs, one for writing CD-R discs and another for writing CD-RW discs. Speed ratings vary from 1x to 52x, where 1x means that a CD is written/read in 'real time' - a 52 minute audio CD would take about 52 minutes to create at 1x speed, and about 1 minute at 52x speed.
The data can be written to the disc in a variety of formats to create an audio CD, a data CD, a video CD or a photo CD. The audio CDs should play on most standard audio CD equipment and the video and photo CDs will play on many consumer DVD players.
Many CD writers (also known as 'burners') are now combination drives which also function as DVD-ROM drives.
Most DVD-RW drives also have CD-RW capabilities.
Digital Video/Versatile Disk Read Only Memory (DVD-ROM)
This optical drive works on a similar principle to the CD-ROM, with a laser being used to read data stored in pits on the surface of a reflective disk. DVDs are read using a shorter wavelength of light (a red laser, rather than an infra-red one). In addition to having a greater data-density, DVDs may be double sided and may be "dual layer".
DVD's hold about 4.7 gigabytes and dual-layer disks hold 8.4 gigabytes (dual layer equipment and disks are now becoming more affordable)
Other removable media
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
Memory sticks or Flash drives are solid-state NAND flash chips packaged to provide additional memory storage. These drives are quickly replacing floppy disks as a means of transferring data from one PC to another in the absence of a network.
Class 3 Components: Peripherals
Class 3 components are components which allow humans to interface with computers.
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. LCD's in addition to being lighter also use less energy and generate less heat.
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.
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.
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.
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.
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.
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.
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.
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 inteface 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.
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 Mbps.
- FireWire (IEEE 1394) port: This high-speed connection runs at 400Mbps (1394a) or 800Mbps (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 Mbps (= 1Gbps).
- 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.