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Computers Basics

The Fundamental Structure of Computers

	Input => Processor => Output
		     ^
		     |
		     V
		   Memory
								

Input Devices

There are a large number of input devices available for computers. The most common input device is the keyboard. Pointing devices such mice, trackballs, and touch screens are also quite common. Multi-media computers frequently have the ability to input audio information from a microphone and image information from either a video camera or an image scanner. This list is by no means an exhaustive list.

Some devices are both input and output devices. Examples include phone connections (i.e. modems) and removable media disk drives (e.g. floppy disk drives and tape drives.)

Output Devices

There are an equally large number of output devices available for computers. The most common output device is the display screen based on either the cathode ray tube (CRT) or on flat panel displays. The display screen is either color or monochrome (one color.) Additional output devices include printers and speakers. As with the input list device, this list of output devices is not exhaustive.

Memory

Memory is a place in which data (information) is kept. There are two kinds of memory -- primary and secondary. Data can be stored to and retreived from primary memory faster than it stored and retreived from primary memory. In addition, most primary memory will retain its data only as long as electrical power is applied to the computer system, whereas most secondary memory retains its data even when electrical power is not applied. These days, primary memory is typically implememted using Dynamic Random Access Memory (DRAM) integrated circuits (IC's.) Secondary memory is typically either disk drive or tape.

Processor

The processor is used to move data from input devices into primary memory, where the data is manipulated prior to being moved to an output device. Besides being able to move data about, processors can perform the standard arithemtic operations of addition, subtraction, multiplication, and division on data. These days, processors are quite fast and are capable of performing millions of operations per second.

Example 1 -- The caculator

A calculator is computer that is specialized to perform arithmetic operations. Its input device is the keyboard. Its output device is usually a display capable of displaying a single number. Some calculators have a a paper tape output to record the results of previous computations. Generally, calculators only have enough primary memory to store a few numbers and no secondary memory. The processor is not very fast since humans can only enter data into calculator very slowly.

Example 2 -- The video game computer

The video game computer is a computer that has been specialized to play video games. Its input device is two or more game controllers, which typically consist of a several buttons and the some approximation to a joystick for specifying directions. The output device is a television which supplies a color image of the game and some sound. Many game computers have input and output devices that are specifically adapted for game playing. Typically video game computers have some primary memory and no secondary memory. In order to keep costs down, the processor in a video game computer is faster than the one in a calculator, but no where near the fastest processor available.

Example 3 -- The personal computer

The personal computer (PC) is a full fledged computer which is quite general in its capabilities. These days a PC has a keyboard and mouse/trackball for input devices. Desktop PC's are still using cathode ray tubes (CRT's) for output displays and portable PC's are using flat panel technology. There is an enormous number of other input and output devices available for PC's. PC's typically have quite a bit of both primary and secondary memory. The processor on a PC is now quite fast.

Hardware vs. Software

A useful analogy for understanding the difference between computer hardware and software is the player piano. A player piano is a piano that can automatically play music. The music to be played is encoded on a scroll of paper by punching holes -- each time a key is to be depressed in the music a corresponding hole is punched in the scroll at an appropriate location. Each time a different piece of music is to be played in a player piano, a scroll containing the music is inserted into the player piano and the piano is started.

[A picture of a player piano would be nice to insert here.]

With the player piano analogy, the piano corresponds to hardware and the scrolls of music correspond to software (i.e. programs.) While piano's are designed by mechanical engineers and music is composed by musicians, computer systems are designed by electrical engineers and software is generally written by computer programmers. People who specialize in the design of computer hardware are called hardware engineers and people who specialize in producing software are called software engineers (i.e. computer programmers.)

In the three computer examples above, where are the programs? For a calculator, there is no program per se, since the human operator manually causes each operation to occur. In the player piano analogy, this manual operation corresponds to a playing music directly on the keyboard. For the video game computer, the program is typically supplied on a game catridge, whose contents are specified by a computer programmer. For the personal computer, the software is also written by a computer programmer and it is typically distributed on either a floppy disk or a compact disk.

Quick Summary

• the four basic components of a computer:
  • input devices
  • output devices
  • memory
  • processor
• three examples of computers:
  • a calculator
  • a video game computer
  • a personal computer
• the terms hardware, software, program, and programmer.

The topic of numbers is discussed in the next section.

Copyright 1993 (c) Wayne C. Gramlich. All Rights Reserved.

Limited copy permission is granted. Comments, corrections, and cross references are solicited. There are currently no known cross references.