A personal computer (PC) is a computer whose price, size, and features make it suitable for personal use. Personal computers are intended for use by one user, as compared with servers. A personal computer, for example, will typically include the ability to play music and display graphics quickly. A server, on the other hand, is intended to be accessed by many users at once over a network; it is unlikely to include sound or fancy display capability, but instead may be configured with additional memory or network connections and a faster processor.
The term personal computer entered common use when small, personally affordable computers became available in the late 1970s. The original PCs were made by Apple Computer with their Apple I and II, Tandy Radio Shack with the TRS-80, and Commodore International with the Commodore PET and Commodore 64. Building on the success of these earlier efforts, IBM in 1983 introduced the IBM PC. This development prompted aspiring computer manufacturers such as Compaq to legally reverse engineer the IBM BIOS (the only hardware on the original PC that was proprietary), thus spawning an entire industry devoted to manufacturing "clones." Clones (more technically IBM compatible PCs) were capable of running the same Disk Operating System as the original IBM PC but on hardware components manufactured by other companies besides IBM.
Personal computers tend to be operated by one user at a time to perform word processing, internet browsing, faxing, e-mail and other digital messaging, multimedia playback, video game play, computer programming, etc. This is in contrast to most other consumer electronics, which tend to specialize in only a few functions, but tend to outperform general purpose PCs at those tasks. As a result, a video game console (for example) can generally play video games better than an equally-priced computer, but can't do any of a PC's other functions.
The user of a modern personal computer may have significant knowledge of the operating environment and application programs, but is not necessarily interested in or capable of programming for the computer. Therefore, most software written primarily for personal computers tends to be designed with simplicity of use, or " user-friendliness" in mind. However, the software industry continuously provides a wide range of new products for use in personal computers, targeted at both the expert and the non-expert user.
Types of Personal computers
Personal computers are generally divided into categories based on their size, portability, and capabilities.
- Desktop computers, frequently simply called desktops, are the largest personal computers. Often they are designed to fit on or under a desk. They frequently have the most expansion capabilities and tend to be the fastest, due to the looser size and heat constraints compared to other types of personal computers. They tend not to include integrated monitors, speakers, keyboards, or other devices, using expansion ports to connect those components.
- All-in-One computers (often abbreviated AIO) are similar to desktop computers, but tend to integrate some external components into one package. In a desktop, the monitor, tower case, and speakers would be separate components connected by cables, while in an AIO, they would be combined into one package, often by building the computer behind the screen. One of the most well-known AIOs is the Apple iMac. An AIO tends to be less powerful and less expandable than a traditional desktop, as it suffers from the same engineering constraints as a portable computer (namely size and weight).
Portable computers are designed for portability, and so are lighter than desktops. They tend to be slightly more expensive than similarly equipped desktops, due to space and heat constraints. Most portable computers contain batteries so that they can be used for short periods without access to an electrical outlet.
- Laptop computers (also called notebook computers) are small personal computers designed for mobility. Usually all of the peripherals needed to operate the laptop are built in to a single unit. They are operated with a keyboard and mouse, and are often nearly comparable to similar desktop computers in terms of processing power.
- Tablet computers are computers that feature a touch screen. These tend to be slightly smaller than laptops. They are often operated with a stylus or a pen instead of a keyboard and mouse, although some models do offer both forms of input. They are generally slightly more expensive than non-tablet laptops.
- Ultra-Mobile PCs (UMPC) bridge the gap between laptops/tablets and PDAs. With a maximum screen size of 7-8 diagonal inches (16-20 cm), they are much smaller than even the smallest laptops at 10-11 diagonal inches, and far smaller than the average 14-15 inch laptop. UMPCs use touch screens, and can run most applications tablets can run. Though far less powerful than most laptops, they can run versions of most computer applications.
- Personal digital assistants (PDAs) are handheld devices that share many traits with other portable computers. They are often used for checking email or calendering, but lack the versatility of computers, and are limited in terms of their software choices. They are often smartphones, and are sometimes considered a consumer electronics device.
Most personal computers are standardized to the point that purchased software is expected to run with little or no customization for the particular computer. Many PCs are also user-upgradable, especially desktop and workstation class computers. Devices such as main memory, mass storage, even the motherboard and central processing unit may be easily replaced by an end user. This upgradeability is, however, not indefinite due to rapid changes in the personal computer industry. A PC that was considered top-of-the-line five or six years prior may be impractical to upgrade due to changes in industry standards. Such a computer usually must be totally replaced once it is no longer suitable for its purpose.
The hardware capabilities of personal computers can sometimes be extended by the addition of expansion cards connected via an expansion bus. Some standard peripheral buses often used for adding expansion cards in personal computers are PCI, AGP (a high-speed PCI bus dedicated to graphics adapters), and PCI Express. Most desktop personal computers have multiple physical PCI expansion slots and a PCI Express (PCIe) bus and one or more expansion slots. Some motherboards contain an AGP bus instead of a PCIe bus, but PCIe has mostly replaced AGP.
The motherboard (or mainboard) is the primary circuit board for a personal computer. Many other components connect directly or indirectly to the motherboard. Motherboards usually contain one or more CPUs, supporting circuitry and ICs for CPU operation, main memory, and facilities for initial setup of the computer immediately after being powered on. Boot firmware or a BIOS is often held in a small piece of non-volatile memory, such as Flash memory.
With high-performance processors and sometimes memory, component-specific cooling fans may be above the component on the motherboard, with the heat sink and fan being mechanically locked to the component socket on the motherboard. Installing a large, heavy cooling assembly over a processor easily may be the most physically difficult part of assembling a PC.
Additionally, it contains connectors for hard drives and optical or floppy drives. In many portable and embedded personal computers, the motherboard houses nearly all of the PC's core components. Often a motherboard will also contain one or more peripheral buses and physical connectors for expansion purposes. Some higher-end motherboards have a secondary daughter board attached to provide further expandability or to satisfy space constraints.
Especially in modular "tower" computers, the motherboard is as important as a place of interconnection as a place where the processor and memory operate. The power supplies often cable to the motherboard, from which power is supplied to cards that plug into PCI and the like. Depending on the disk type, it may get all its power from the motherboard, or, when there are multiple disks of the same type, the first may get power from the motherboard, and then the other disks are "daisy-chained" to pass both signals and power.
In laptops, the motherboard may be sufficiently "all-in-one" that almost any repair may need it to be replaced, which, if the computer is a year or so old, may not be economic. It can be frustrating when the problem is no more than an external power connector at the edge of the motherboard, which lines up with the external jack on the case into which the external power supply/battery charger, which breaks loose due to power connector stresses. An occasional highly skilled technician sometimes can solder it back in place, but that is not the factory recommended technique.
Central processing unit
The central processing unit, or CPU, is the part of the computer that executes operations. Computer software programs, including the operating system, consists of millions of processor instructions encoded in binary. Nearly all PCs contain a type of CPU known as a microprocessor. The microprocessor often plugs into the motherboard using one of many different types of sockets. IBM compatible PC computers use an x86-compatible processor. Intel makes most of the processors in personal computers, with AMD being it's closest competitor. Via and Transmeta also make x86 processors. Other types of computers might use Power PC, SPARC or other types of CPUs, however nearly all computers sold to home users use x86 processors.
Personal computers generally have only a single processor package, which may have two or four cores. Each core is essentially an independent processor. Each processor package fits into a socket. Workstations and servers may have multiple sockets, but nearly all personal computers have only a single socket.
A PC's main memory place (or primary storage) is fast storage space that is directly accessible by the CPU, used to store the currently executing program and immediate data. PCs use semiconductor random access memory such as SDRAM as their primary storage. Main memory is usually much faster than mass storage devices like hard disks or optical discs, but cannot retain data without power and is more expensive than mass storage. Therefore, it is not generally suitable for long-term or archival data storage.
Mass storage stores programs and data without consuming power. Although semiconductor flash memory has dropped in cost, the prevailing form of mass storage in personal computers is still the electromechanical hard disk.
If the mass storage controller (often on the motherboard) provides for expandability, a PC may also be upgraded by the addition of extra hard disks or removable storage drives. Standard internal storage device interfaces are ATA and Serial ATA, with SATA being the faster of the two. Other types of internal storage device interfaces include SCSI and CF+ Type II. A hard drive usually takes up a 3.5 inch or 2.5 inch bay inside a computer.
Removable storage drives include DVD, CD, and floppy disk drives, as well as flash card readers. In most cases, removable storage drives are bigger than hard drives, requiring a 5.25 inch bay. Drives are generally named by what sort of actions they can perform on a type of media. For instance, a "DVD-ROM" drive can read DVDs, because "ROM" stands for "Read-Only Memory". A "CD-R" drive can record once to a CD, and also read CDs, because the "-R" stands for "recordable". A "CD-RW" drive can read and rewrite CDs, because "-RW" stands for "re-writeable".
Graphics - Video card
The graphics processing unit (GPU) is responsible for handling the graphics output of the computer, usually to a monitor. A GPU contains a special-purpose processor and its own memory. GPUs usually handle one or two outputs, often in forms like VGA, DVI, and S-Video. In some computers, GPUs can also handle other functions, such as video decoding.
A graphics unit can be dedicated or integrated. A dedicated graphics unit is normally housed on an expansion card and connected to the motherboard by an expansion slot, such as PCIe or AGP, and includes dedicated RAM for the graphics coprocessor to use. An integrated graphics solution borrows RAM from the processor to do its work. Generally, lower-end PCs or smaller PCs tend to have integrated graphics solutions, while midrange or high-end PCs have dedicated graphics cards. Gaming PCs sometimes include more than one graphics card.
The sound card is responsible for the input and output of computer audio. A PC sound card generally has at least two (Line-In/Line-Out) stereo ports. Like the GPU and ethernet card, the sound card can be both dedicated or integrated.
The power supply is needed to deliver the electricity to each of the components of the PC, either individually or through the motherboard. It converts AC power to a few different voltages of DC power. Each different voltage line is sometimes referred to as a "rail". The consumption of the components and the output of the power supply is limited by the current on each rail. In order for the PC to perform at its peak, the output of the power supply on each rail must be greater than or equal to the sum of the maximum consumptions of the components using that rail. Usually, the limiting rail is the +12V rail because this feeds the CPU, the GPU, and the drives.