The Open Encyclopedia Project

Overview

Computers form the underpinning of modern society, whether as "typical" machines, including PCs and Macs, or as larger mainframe systems, at the heart of large corporations. Almost all domestic "intelligent" devices include some form of computer, as an embedded device - including video recorders, microwave ovens and televisions. The use of the word computer originally was given to people that performed long tedious sequences of mathematical calculations. Now the word is used to refer to an electronic device that processes data in digital format, using a complex set of operations executed by a Central Processing Unit (CPU), which is the heart of the modern day computer. Modern computers are based on the von Neumann architecture. This is due to a 1946 paper that was written by John von Neumann along with Arthur W. Burks and Hermann H. Goldstine. The paper was titled "Preliminary Discussion of the Logical Design of an Electronic Computing Instrument". It described the basic architecture and sub-systems that comprise the structure of a general purpose computing device. John von Neumann felt the four most basic sub-systems a general computing device required were an arithmetic processing unit, a memory storage unit, a master control unit and a way to interface with a human operator. All of these sub-sections and more are important in a modern computer.

Central Processing Unit

The Central Processing Unit is the brain of the computer. It is responsible for executing the machine code instruction set that controls the system. The CPU fetches these instructions from memory and these instructions control every aspect of the computer's operations. Some of the tasks performed by these instructions are: - Writing and reading data, to and from memory - Writing and reading the ports in the system. These ports are used to interface with the peripheral devices contained in the system (e.g. - the keyboard, the serial and parallel ports, etc.) - Controlling the arithmetic processing unit to execute mathematical operations

Memory

The memory sub-system is the work area the CPU uses for reading instructions to execute, and for the reading and writing of data. Memory is frequently referred to as RAM or Random Access Memory. This is because any memory location can be accessed directly through it's address, rather than having to read sequentially through every location to get to a desired address. Another commonly used acronym is ROM which refers to Read-Only Memory. The information kept in memory is typically temporary; it disappears when the system is shut off or rebooted. However there are some forms of memory where the information is persistent. For example Electrically Erasable Programmable Read-Only Memory or EEPROM's, are memory chips where information is burned into the chip and will persist even after the loss of power or a reboot. Memory that can retain its information permanently is known as non-volatile memory. ROM's and EEPROM's are important because they contain machine code instructions that basically jump start the computer. These instructions are also known as the Basic Input-Output System or BIOS. If these non-volatile memory chips did not exist in a computer, it would just sit there and do nothing when first powered on. (See the section titled BIOS below.)

BIOS

The Basic Input-Output System BIOS is responsible for initializing a computer system into a usable state. The primary task performed by the BIOS during startup is to check the status and initialize the most important sub-systems and peripherals in the computer system such as memory, the hard disk and more. Any problems that occur during startup are reported to the user. It also is responsible for initializing the operating system (See the section titled Operating System).

Operating System

The operating system contains the software that comprises the core functionality of a computer. The operating system or OS contains large libraries of machine code that are responsible for interfacing with every sub-system in the computer. For example the code for reading and writing the hard disk, writing information to the monitor, interfacing with the keyboard, and much more are all contained in the operating system. Most high-level or application level software uses the operating system to perform any hardware related tasks. The operating system frees the application level software developer from needing to have detailed knowledge of the hardware platform the software is running on. Instead, the software application makes calls to the operating system's API or Application Program Interface. The operating system then executes the necessary machine code instructions to interface with the desired sub-system or peripheral. For example, writing text to the computer's monitor.

Peripherals

Peripherals are the hardware devices in a computer that perform specialized tasks and are external to the main computer's motherboard. Peripherals can be connected directly into slots on the motherboard, or through ports such as the serial port, the parallel port, USB or Universal Serial Bus ports, and many other kinds of connections. Some popular examples of a peripheral are: - Hard disks - Keyboards - The Mouse - Scanners - Sound cards - Graphics cards - Network interface cards or NIC's When a peripheral reaches a certain level of popularity, like network interface cards, they are frequently integrated directly into the computer's motherboard.

Monitor

The monitor is the primary display device that communicates visual information in the form of text and graphics to the user. Some popular monitor types are: - Cathode Ray Tubes or CRT's - Liquid Crystal Displays or LCD's - Plasma screens

Input Device

Most computers need a way to allow a human operator to communicate with it. For example to give it instructions, enter data, or write software programs. When people think of using a computer the keyboard frequently comes to mind. However there are many other kinds of input devices. For example: - Microphones for speech and other audio input - Eye blinks sensors so the severely handicapped can provide input to a computer - Scanners which allow documents to be digitized and stored on a computer - Touch screens which are popular on Personal Digital Assistant's or PDA's Even more innovative input devices are on the horizon such as virtual reality gloves with tactile feedback and others.