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What is a Computer?

A computer is a device that accepts data, then performs arithmetic or logical operations that manipulate or change the data, and finally produce new results from that data. Given that definition, you might think there are many machines or devices that qualify as a computer – and you’d be right. Computers come in many shapes and sizes. Commonly, they are grouped into four types: the personal computer, the minicomputer, the mainframe computer, and the supercomputer.

The Personal Computer

For many people, the path to computer literary begins with the personal computer, so that is our primary focus here. The personal computer, or microcomputer as it is sometimes called, is(1)one designed for use by a single individual, (2) usually small enough to fit on a desktop, and (3) affordable enough for the average person. The personal computer is sometimes called a microcomputer, reflecting the fact that it is smaller than a mainframe of a minicomputer. Today, we commonly use the term personal computer (or PC) generally to refer to many different kinds of microcomputers. This includes the IBM PC, the Apple Macintosh, the Commodore Amiga, and many others.

Personal computers come in many sizes. Besides the common desktop machine, there are portable, laptops, notebooks, and palmtops. The most powerful models are called workstations, which have the power and capabilities of a minicomputer.

The first personal computers were like the old Volkswagen beetle: they came with only the bare essentials. Their owners had to know a lot more about electronics than today’s personal computer users. In 1977, Apple and Tandy/Radio Shack became the first companies to introduce personal computers to the mass consumer market. Radio Shack’s management wasn’t sure there would be much interest in personal computers when the TRS-80 Model I came off the assembly line, so they only made enough so each retail store would have one. If it didn’t sell, the store could use it for inventory or something, they reasoned. Needless to say, it sold very well and today Tandy is one of the leading personal computer suppliers.

A state-of-the-art personal computer has a system unit, where the computer’s electronic and mechanical are housed. The keyboard is used to enter data and instructions. The monitor or video display screen is where you see your work. A separate printer provides a finished copy of the results. These hardware components are common to all computers, large and small. Large computers often fill many cabinets and can have hundreds of keyboards and monitors, so more than one person can use them at once.

The Minicomputer

The minicomputer is a versatile, medium-sized computer designed so that more than one person can use it at the same time. It was introduced as a smaller, less expensive alternative to the mainframe. Early minis were designed for use in a variety of special-purpose tasks (manufacturing, engineering, science, and process control, for example):

*Providing instructions for manufacturing equipment

such as presses or robots.

*Use in guidance systems for aircraft

*Measuring seismographic fluctuations in dangerous

mines.

*Use in control processes such as keeping a constant

temperature for cooking vats of soup, spaghetti

sauce, or chocolate.

Yet over time, the mini became a viable computer for business purposes, serving the needs of a small to medium-size company or a department or division of a larger company.

Minis are often connected to other minis, and are commonly used to provide connections between mainframe computers and personal computers. It is a good idea to remember that many of the sharp distinctions between mainframes and minis and between minis and powerful personal computers have been blurred by technological advances.

The mini was designed by Kenneth W. Olsen, an MIT graduate who went on to found Digital Equipment Corporation (DEC), the world’s second-largest computer company. In 1959, Digital introduced the PDP-1 (for Programmed Data Processor). At a time when typical computer systems sold for over $1 million, the PDP-1’s price tag of $120,000 shocked the industry. Of course, it was not able to perform all the tasks of a mainframe but it was a true computer nonetheless. It was followed by several other PDPs, the last of which, the PDP-11, led to the VAX, introduced in 1975, which is now the most widely used family of minicomputers in the world. Today, there are minis of all sorts; some are as large or as powerful as mainframes, while others fit on a desktop.