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A computer is literally a machine that computes mathematical operations.
When one thinks of the most-common form of computer, the desktop PC, the fact that this device is essentially a very powerful calculator does not seem accurate. However, all of the functions that are performed by any computer, including a PC, are the result of mathematical operations.

This is because computers represent information as 1′s and 0′s. It is the sequence and number of the 1′s and 0′s that tell a computer what letters, symbols, and numbers make up the data it stores as well as the instructions it is to complete. Everything that a computer does is the result of the deciphering of 1′s and 0′s.

Physically, computers are usually a collection of very small electrical devices that reside on a common circuit board. These devices are called ‘microchips,’ Usually made of silicon, microchips contain millions, or even billions, of tiny transistors that are used to represent 1′s (on) and 0′s (off). Most microchips have specific purposes or contributions to the computer system, with the CPU being the main processor that controls all of the functions of the computer.

In order to process information, computers must have storage devices, both for short-term and long-term storage. Short-term storage is required for the computer to hold information for processing, and long-term storage is needed to keep the information while it’s not being processed.

Short-term, high-speed, computer memory is usually provided by microchips that lose their data when the power is turned off. Long-term memory is generally slower and is kept on magnetic media such as hard drives, optical memory such as CD’s or special microchips, (flashdrives), that keep their memory even when the power is turned off.

As computers require human instruction, they must have either a communications port/method or a monitor with inputs such as a mouse and keyboard. A communications port/method allows for the computer to connect to another computer that has a display with inputs. Most desktop PCs have a display with inputs as well as several kinds of communication ports, including Serial ports, USB ports, Ethernet ports, and Parallel ports.

It is important to note that the words ‘USB’, ‘Serial’, ‘Ethernet’ and ‘Parallel’, and several others, refer to the physical design of the receiver attached to the computer and to the cables that work with these receivers. For each of these receivers, the computer must have instructions (or ‘programs’) that tell it how to send and receive data via these ports. Generally, these instructions are contained in the computer’s ‘operating system’ which is the collection of instructions that provide the foundation for the computer’s functions.

A personal computer usually has a screen and keyboard. It probably has one or more hard drives, a CD/DVD-ROM and maybe even a floppy disk. Some of these devices are run by controller cards that plug into the motherboard, (the mainboard of the computer), and help the computer drive them; others are run by specialized chipsets directly on the motherboard that fulfill the same function as a controller card. The processor and memory also live on the motherboard. It is the heart of a personal computer.

Most laptops have specialized chipsets on the motherboard whereas desktop computers usually have some controller cards, although in recent years the more common functions have resulted in specialized chipsets being added to the motherboard and the need for plug in controller cards has been greatly diminished. The keyboard, whether laptop or desktop, is too simple to need a separate card. Its controller is usually a part of the keyboard chassis itself.

The parts of the computer inside the case are connected by a bus. In a desktop computer, the bus is what you plug your controller cards into (the video card, specialized disk controllers, sound cards, etc., if you have any such things), although it also includes printed circuitry on the motherboard that connects the built-in functions to the processor. On a laptop, the bus is probably just more printed circuit etchings on the mother board, extending to all the built-in sub-systems. In any event, the bus is the data highway between the processor, the screen, the disk, and everything else.

(If you\’ve seen references to ‘ISA’, ‘PCI’, and ‘PCMCIA’ in connection with PCs and have not understood them, these are bus types. ISA is, except in minor details, the same bus that was used on IBM’s original desktop PCs in 1980; it is seldom used now. PCI, for Peripheral Component Interconnection, is the bus used on most modern desktop PCs. PCMCIA is a variant of ISA with smaller physical connectors used on laptop computers.)

The processor, which makes everything else go, can’t actually see most of the other pieces directly; it has to talk to them over the bus. The only subsystem that it has direct access to is the memory (RAM). In order for programs to run they have to be in memory.

When the computer reads a program or data off the disk, what actually happens is that the processor uses the bus to send a disk read request to the disk controller. Some time later the disk controller uses the bus to signal the processor that it has read the data and put it in a certain location in memory. The processor can then look at that data.

The keyboard and screen also communicate with the processor via the bus, but in simpler ways.

[This post was adopted, (with some modification), from a chapter written several years ago as part of The Linux Documentation Project. In spite of its age and authorship, it has general applicability to most personal computers being used today, whether running Windows, Mac OS, Linux or some other system. The original text should be available at http://tldp.org/HOWTO/Unix-and-Internet-Fundamentals-HOWTO/anatomy.html.]‘);