Computers: Taking a Brief Look

By ClockWeb

Computer , a device capable of performing a series of arithmetic or logical operations. A computer is distinguished from a calculating machine, such as an abacus or electronic calculator, by being able to store a computer program (so that it can repeat its operations and make logical decisions) and to store and retrieve data without human intervention. Computers are classed as analog or digital. An analog computer operates on continuously varying data; a digital computer performs operations on discrete data. An analog computer represents data as physical quantities and operates on the data by manipulating the quantities. In a complex analog computer, continuously varying data are converted into varying electrical quantities and the relationship of the data is determined by establishing an equivalent relationship, or analog, among the electrical quantities. Analog computers have been nearly completely obsoleted by more effective digital computers. Within a digital computer, data are expressed in binary notation, i.e., by a series of "on-off" conditions that represent the digits "1" and "0." A series of eight consecutive binary digits, or bits, is called a byte and allows 256 "on-off" combinations. Each byte can thus represent one of up to 256 alphanumeric characters. Arithmetic and comparative operations can be performed on data represented in this way and the result stored for later use. Digital computers are used for reservation systems, scientific investigation, data-processing applications, and electronic games.

Hardware. The four major physical components, or hardware, of a computer are the central processing unit (CPU), main storage, auxiliary storage, and input/output devices. Computer operations are performed in the CPU, which contains the logic circuits for arithmetic and logical operations and for control of the other units that make up a computing system. The CPU also contains the registers, a relatively small number of storage locations that can be accessed faster than main storage and are used to hold the intermediate results of calculations. The main storage is contained in the storage unit, or memory, of the computer. Main storage-once made up of vacuum tubes and later of magnetic cores, each tube or core representing one bit-is now made up of tiny Integrated Circuits, each of which contains thousands of semiconductors. Each semiconductor represents one bit. Programs and data that are not currently being used in main storage can be saved on auxiliary storage, or external storage. Although punched paper tape once served this purpose, the major materials used today are magnetic tape and magnetic disks.

Diagram of Computer Processing I/O

Two areas of continuing research are bubble memories and laser storage. A bubble memory has no moving parts, which improves its reliability; in this technology, a rotating magnetic field moves a magnetic "bubble" (each bubble representing a bit) along loops made of small bars of permalloy. Because the bubbles are so minute in size, huge volumes of data can be stored in tiny spaces. Laser storage involves an array of small holograms, each capable of representing a "page" of binary data. When illuminated by laser light, each page generates a real image of light and dark spots; this falls on a detector array that converts it into electrical signals. Data are entered into the computer and the processed data made available via input/output devices. All auxiliary storage devices are used as input/output devices. For many years, the most popular input/output medium was the punched card. Although this is still used, the most popular input device is now the computer terminal and the most popular output device is the high-speed printer. The CPU, main storage, auxiliary storage, and input/output devices collectively make up a system. Multiple systems may be tied together by telecommunications links to form a network.

Software. The computer program, or software, controls the functioning of the hardware and directs its operation.