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Five Types of Computer Systems

Computers are classified into microcontrollers, microcom­puters, minicomputers, mainframe computers, and supercomputers.

Microcontrollers are embedded in machines such as cars and kitchen appliances.

Microcomputers may be personal computers (PCs) or workstations. PCs include desktop and floor-standing units, laptops, notebooks, subnotebooks, pocket PCs, and pen computers. Workstations are sophisticated desktop micro­computers used for technical purposes.

Minicomputers are intermediate-size machines.

Mainframes are the traditional size of computer and are used in large companies to handle millions of transactions.

The high-capacity machines called supercomputers are the fastest calculating devices and are used for large-scale projects. Supercomputers have two designs: vector processing and massively parallel processing.

Any of these types of computers may be used as a server, a central computer in a network.

Generally speaking, the larger the computer, the greater its processing power. Computers are often classified into five sizes—tiny, small, medium, large, and super large.

· Microcontrollers—embedded in "smart" appliances

· Microcomputers—both personal computers and workstations

· Minicomputers

· Mainframe computers

· Supercomputers


In this chapter, we give you a bit more information about these categories.


Microcontrollers, also called embedded computers, are the tiny, specialized microprocessors installed in "smart" appliances and automobiles. These microcontrollers enable, for example, microwave ovens to store data about how long to cook your potatoes and at what temperature.

Microcomputers: Personal Computers

Microcomputers are small computers that can fit on or beside a desk or are portable. Microcomputers are considered to be of two types: personal com­puters and workstations.

Personal computers (PCs) are desktop, tower, or portable computers that can run easy-to-use programs such as word processing or spreadsheets. PCs come in several sizes, as follows.

Even though many personal computers today are portable, buyers of new PCs often opt for nonportable systems, for rea­sons of price, power, or flexibility. For example, the television-tube-like (CRT, or cathode-ray tube) monitors that come with desktops have display screens that are easier to read than those of many portables. Moreover, you can stuff a desktop's roomy system cabinet with add-on circuit boards and other extras, which is not possible with portables.

Desktop PCs are those in which the system cabinet sits on a desk, with keyboard in front and monitor often on top. A difficulty with this arrange­ment is that the system cabinet's "footprint" can deprive you of a fair amount of desk space. Tower PCs are those in which the system cabinet sits as a "tower" on the desk or on the floor next to the desk, giving you more usable desk space.

· A laptop computer is a portable computer equipped with a flat display screen and weighing 8-20 pounds. The top of the computer opens up like a clamshell to reveal the screen.

We describe the differences between display screens elsewhere. Here we will simply say that flat screens don't provide the quality of the monitors found with desktop computers (although that is changing). However, most laptops can be hooked up to standard desktop-type monitors so that you don't lose display quality.

* Notebooks: A notebook computer is a portable computer that weighs 4-7.5 pounds and is roughly the size of a thick notebook, perhaps SVz by 11 inches. Notebook PCs can easily be tucked into a briefcase or back­pack or simply under your arm.

Notebook computers can be just as powerful as some desktop machines. However, because they are smaller, the keys on the keyboards are closer together and harder to use. Also, as with laptops, the display screens are more difficult to read.

* A subnotebook computer weighs 2.5-4 pounds. Clearly, subnotebooks have more of both the advantages and the disadvantages of notebooks

· Pocket personal computers, or handhelds, weigh about 1 pound or less. These PCs are useful in specific situations, as when a driv­er of a package-delivery truck must feed hourly status reports to company headquarters. Another use allows police officers to check out suspicious car license numbers against a database in a central computer. Other pocket PCs have more general applications as electronic diaries and pocket orga­nizers.

Pocket PCs may be classified into three types:

(1) Electronic organizers are specialized pocket computers that mainly store appointments, addresses, and "to do" lists. Recent versions feature wireless links to other computers for data transfer.

(2) Palmtop computers are PCs that are small enough to hold in one hand and operate with the other.

(3) Pen computers lack a keyboard or a mouse but allow you to input data by writing directly on the screen with a stylus, or pen. Pen computers are useful for inventory control, as when a store clerk has to count merchandise,- for package-delivery drivers who must get electronic signatures as proof of delivery; and for more general purposes, like those of elec­tronic organizers and PDAs.

Personal digital assistants (PDAs), or personal communicators, are small, pen-controlled, handheld computers that, in their most developed form, can do two-way wireless messaging.

We explain more about notebooks, subnotebooks, and pocket PCs, and their usefulness, in the Experience Box at the end of this chapter.

What is the one thing besides their light weight that makes portable com­puters truly portable? The answer: batteries. A typical notebook's batteries will keep it running about 3-5 hours, a subnotebook's about 3 hours. The record holder seems to be 8 hours and 45 minutes on a standard nickel metal hydride battery.8 Then the PC must be plugged into an AC outlet and charged up again. Some travelers carry spare battery packs.

In the works is a zinc-air battery that can run a laptop for up to 12 hours without a recharge. However, refinements are still being made.

Microcomputers: Workstations

Workstations look like desktop PCs but are far more powerful. Traditionally, workstations were sophisticated machines that fit on a desk, cost $10,000-$150,000, and were used mainly by engineers and scientists for tech­nical purposes. However, workstations have long been used for computer-aided design and manufacturing (CAD/CAM,), software development, and scientific modeling. Workstations have caught the eye of the public mainly for their graphics capabilities, such as those used to breathe three-dimensional life into toys for the movie Toy Story.

Two recent developments have altered the differences between worksta­tions and PCs:

* Decline in workstation prices. A workstation that not long ago cost $15,000 or more is now available for under $5000, which puts it within range of many PC buyers.

* In 1993 Intel introduced the Pentium chip - in 1994 Motorola (with IBM and Apple) introduced its PowerPC chip. Both of these very powerful microprocessors are now found in PCs. In addition, Microsoft introduced Windows NT, the first operating system designed to take advantage of more powerful microprocessors.

You might deduce from this that, if PCs are becoming more powerful, then workstations are becoming more powerful still—and indeed they are. Over the past 15 years the fastest workstations have increased in speed a thou­sand fold. They have been cutting into the sales not only of minicomput­ers and mainframes but even of supercomputers. These large machines have become vulnerable particularly since workstations can now be harnessed in "clusters" to attack a problem simultaneously


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.


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.



Gregory Chudnovsky, 39, with the help of his older brother, David, built a supercomputer in the living room of his New York City apartment. Seven feet tall and 8 feet across, the supercomputer was put together from mail­ order parts and cost only $70,000 [compared to $30 million for some com­mercial supercomputers).

The brothers, both mathematicians and former citizens of the Soviet Union, have found some drawbacks to their homemade machine, which they named "m zero." They must keep the computer, along with 25 fans, running day and night. They must make sure the apartment's lights are turned off as much as possible, to prevent blowing the wiring in the living unit. "The building superintendent doesn't know that the Chudnovsky brothers have been using a supercomputer in Gregory's apartment," reports journalist Richard Preston, "and the brothers haven't expressed an eagerness to tell him." Still, the machine makes their lives more convenient. The "m zero" performs computations that make up the basis of many of the scholarly papers and books they write on number theory and mathematical physics.

Most supercomputer users aren't as resourceful as the Chudnovskys and must buy their equipment from manufacturers. Typically priced from $225,000 to over $30 million, supercomputers are high-capacity machines that require special air-conditioned rooms and are the fastest calculating devices ever invented.

Supercomputer users are those who need to model complex phenomena. Examples arc automotive engineers who simulate cars crashing into walls and airplane designers who simulate air flowing over an airplane wing. "Supers," as they are called, are also used for oil exploration and weather forecasting. They can also help managers in department-store chains decide what to buy and where to stock it. Finally, they have been used to help redesign parachutes, which are surprisingly complex from the standpoint of aerodynamics. The supercomputer simulates the flow of air in and around the parachute during its descent. In 1995 Intel announced plans to build a supercomputer that would enable scientists to simulate the explosion of a nuclear bomb. Supercomputers are designed in two ways:

The traditional design, now 20 years old, is vector processing. In vector processing, a relatively few (1-16) large, highly spe­cialized processors run calculations at high speeds. The drawback is that tasks are accomplished by a single large processor (or handful of proces­sors] one by one, creating potential bottlenecks. In addition, the proces­sors are costly to build, and they run so hot that they need elaborate cool­ing systems.

Massively parallel processors! The newer design is called massively parallel processing (MPP), which spreads calculations over hundreds or even thousands of standard, inexpensive microprocessors of the type used in PCs. Tasks are parceled out to a great many processors, which work simultaneously. The reason the Chudnovsky brothers were able to build their super so cheaply was that they used standard microprocessors avail­able for PCs in an MPP design.

A difficulty is that MPP machines are notoriously difficult to program, which has slowed their adoption. Still, with the right software, 100 small processors can often run a large program in far less time than the largest supercomputer running it in serial fashion, one instruction at a time.

Massively parallel processing might seem as powerful as one could expect. However, fiber-optic communications lines have made possible supercomputing power that is truly awesome. In 1995 the National Science Foundation and MCI Communications, the nation's No. 2 long-distance provider, established a Very-high-speed Backbone Network Service (VBNS) that links the five most important concentrations of supercomputers into what they call a nationwide "metacenter." Each of these locations has more than one supercomputer (Cornell and Champaign-Urbana have six each). With this arrangement a scientist sitting at a terminal or workstation any­where in the country could have access to all the power of these fast machines simultaneously.


The word "server" does not describe a size of computer but rather a partic­ular way in which a computer is used. Nevertheless, because of the princi­pal concerns of this book—the union of computers and communications— servers deserve separate discussion here.

A server, or network server, is a central computer that holds databases and programs for many PCs, workstations, or terminals, which are called clients. These clients are linked by a wired or wireless network. The entire network is called a client/server network. In small organizations, servers can store files and transmit electronic mail between departments. In large orga­nizations, servers can house enormous libraries of financial, sales, and prod­uct information. The surge in popularity of the World Wide Web has also led to an increased demand for servers at tens of thousands of Web sites.

Network servers appear in a variety of sizes. As one writer points out, they may consist of "everything from souped-up PCs selling for $10,000 to main­frames and supercomputer-class systems costing millions." For more than a decade, he points out, the computer industry was driven by a rush to put stand-alone microcomputers in offices and homes. Now that we are far along in putting a PC on every desktop, the spotlight is shifting to computers that can do work for many different people at once

On the one hand, then, this puts "big iron"—minis, mainframes, supers— back in the picture. Recognizing this, IBM has combined formerly separate personal, midrange, and mainframe computer units into an umbrella organi­zation called the Server Group. On the other hand, the demand for servers based on microcomputers has made souped-up PCs and Macintoshes a growth industry—and is bringing these machines "close to the power of more expensive minicomputers and mainframes," according to some PC makers.

Now let's move on to look inside computers to see how they work.



Date: 2015-04-20; view: 2801

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