Minicomputers

Minicomputers are machines midway in cost and capability between micro­computers and mainframes. They can be used either as single workstations or as a system tied by network to several hundred terminals for many users.

The minicomputer overlaps with other categories of com­puters. A low-end minicomputer may be about as powerful as a high-end microcomputer and cost about the same. A high-end minicomputer may equal a low-end mainframe.

Traditionally, minicomputers have been used to serve the needs of medium-size companies or of departments within larger companies, often for accounting or design and manufacturing (CAD/CAM). Now many are being replaced by systems of networked microcomputers.

Mainframes

The large computers called mainframes arc the oldest category of computer system. The word "mainframe" probably comes from the metal frames, housed in cabinets, on which manufacturers mounted the computer's elec­tronic circuits.

Occupying specially wired, air-conditioned rooms and capable of great pro­cessing speeds and data storage, mainframes are water- or air-cooled com­puters that are about the size of a Jeep and that range in price from $50,000 to $5 million. Such machines are typically operated by pro­fessional programmers and technicians in a centrally managed department within a large company. Examples of such companies are banks, airlines, and insurance companies, which handle millions of transactions.

Today, one hears, "mainframes are dead," being supplanted everywhere by small computers connected together in networks, a trend known as "down­sizing/' Is this true? The world has an estimated $1 trillion invested in this kind of "big iron"—perhaps 50,000 mainframes, 60% of them made and sold by IBM. But what are the future prospects for people working with main­frames? Although mainframe manufacturers will probably promote new uses for their equipment, there appear to be three trends:

* Massive and repet­itive computing chores, such as maintaining a company's payroll, may best be left on a mainframe rather than moved to a new system.

* Mainframes usually can­not be reprograrnmed quickly to develop new products and services, such as pulling together information about single customers from different divi­sions of a bank. Networks offer the flexibility that mainframes lack because networks are not burdened with an accumulation of out-of-date programming.

* IBM has worked to redesign mainframes, which formerly were essentially custom-built. Now they are being manufactured on an assembly-line basis, making them less expensive. In. addition, the automobile-size machines will be reduced to the size of a desk. Encompassing more recent technology (called parallel processing, described shortly), new mainframes will not require water cooling. As a result, a SI million machine will come down in price to only $100,000.

Despite the trend toward downsizing and using networks of smaller com­puters, mainframe makers such as IBM and Amdahl have continued to ship "big iron" in record amounts. One reason may be that the costs of main­taining a mainframe are actually cheaper (averaging $2300 per user per year, according to one study) than networks of PCs ($6400). Moreover, networks of PCs can't match mainframes for reliability or security of data.

Дата добавления: 2015-11-14