Computers and Computer Systems

A computer is a programmable device that can automatically perform a sequence of calculations or other operations on data once programmed for the task. It can store, retrieve, and process data according to internal instructions. A computer may be either digital, analog, or hybrid, although most in operation today are digital. Digital computers express variables as numbers, usually in the binary system. They are used for general purposes, whereas analog computers are built for specific tasks, typically scientific or technical. The term "computer" is usually synonymous with digital computer, and computers for business are exclusively digital.

ELEMENTS OF THE COMPUTER SYSTEM

The core, computing part of a computer is its central processing unit (CPU), or processor. It comprises an arithmetic-logic unit to carry out calculations, main memory to temporarily store data for processing, and a control unit to control the transfer of data between memory, input and output sources, and the arithmetic-logic unit. A computer is not fully functional without various peripheral devices, however. These are typically connected to a computer through cables, although some may be built into the same unit with the CPU. These include devices for the input of data, such as keyboards, mice, trackballs, scanners, light pens, modems, magnetic strip card readers, and microphones, as well as items for the output of data, such as monitors, printers, plotters, loudspeakers, earphones, and modems. In addition to these input/output devices, other types of peripherals include computer data storage devices for auxiliary memory storage, where data is saved even when the computer is turned off. These devices most often are magnetic tape drives, magnetic disk drives, or optical disk drives.

Finally, for a digital computer to function automatically, it requires programs, or sets of instructions written in computer-readable code. To be distinguished from the physical or hardware components of a computer, programs are collectively referred to as software.

A computer system, therefore, is a computer combined with peripheral equipment and software so that it can perform desired functions. Often the terms "computer" and "computer system" are used interchangeably, especially when peripheral devices are built into the same unit as the computer or when a system is sold and installed as a package. The term "computer system," however, may also refer to a configuration of hardware and software designed for a specific purpose, such as a manufacturing control system, a library automation system, or an accounting system. Or it may refer to a network of multiple computers linked together so that they can share software, data, and peripheral equipment.

Computers tend to be categorized by size and power, although advancements in computers' processing power have blurred the distinctions between traditional categories. Power and speed are influenced by the size of a computer's internal storage units, called words, which determine the amount of data it can process at once and is measured in bits (binary digits). Computer speed is also determined by its clock speed, which is measured in megahertz. Additionally, the amount of main memory a computer has, which is measured in bytes (or more precisely, kilobytes, megabytes, or gigabytes) of RAM (random access memory), plays a role in determining how much data it can process. The amount of memory that auxiliary storage devices can hold also determines the capabilities of a computer system.

THE MICROCOMPUTER

The development of the microprocessor, a CPU on a single integrated-circuit chip, enabled the development of affordable single-user microcomputers for the first time. The slow processing power of the early microcomputers, however, made them attractive only to hobbyists and not to the business market. In 1977, however, the personal computer industry got under way with the introduction of off-the-shelf home computers from three manufacturers.

The term "personal computer" (PC) was coined by IBM with the launch of its PC in 1981. This model became an instant success and set the standard for the microcomputer industry. By the early 1990s personal computers had become the fastest-growing category of computers. This was largely due to the adoption of their use in businesses of all sizes. The availability of these small, inexpensive computers brought computer technology to even the smallest of enterprises.

The most recent category of microcomputer to enter the business world is the portable computer. These small and light—but increasingly powerful—computers are commonly known as laptop or notebook computers. Laptop computers have the same power as desktop personal computers, but are built more compactly and use flat screen monitors, usually using liquid crystal display, that fold down to form a slim unit that fits in a briefcase and usually weigh under 15 pounds. A notebook computer is one that weighs under 6 pounds and may or may not have a full-size keyboard. A pocket computer is a hand-held calculator-size computer. A personal digital assistant is a pocket computer that uses a pen and tablet for input, has a fax/modem card, and is combined with the capabilities of a cellular telephone for remote data communications. Portable computers are increasingly popular among businesspeople who travel, such as executives or sales representatives.

Open Systems

Today, most computer systems are "open"—compatible with computer hardware and software from different manufacturers. In the past, all components of a computer system originated from the same manufacturer. There were no industry-wide standards. As a result, printers, monitors, and other peripheral equipment from one manufacturer would not operate when matched with the computer of another manufacturer. More significantly, software could only run on the specific computer brand for which it was designed. Today, however, "open systems," wherein various equipment from different manufacturers can be matched together, is common. Open systems are especially popular among small business owners because they allow enterprises to upgrade or expand their computer systems more easily and cheaply. Open systems provide business owners with more buying options, enable them to minimize expenses of employee retraining on new systems, and give them greater freedom to share computer files with outside clients or vendors.

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