There are many ways to classify computers. Virtually all modern computers are electronic. Three other ways to classify computers are according to whether they are digital or analog, central or specialized processors, or full- instruction-set or reduced-instruction-set processors.
1. Digital versus Analog :
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A digital computer is one that counts; an analog computer is one that measures. Counting and measuring, which are the most basic types of computation, were with us long before computers existed.
When we observe that there are 15 people in a room, for example, we are counting. Entities; such as people, books, and dollars are capable of being counted.
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When we estimate that there are 10 gallons of fuel in a gas tank, on the other hand, we are measuring; there may actually be 10.0001,9.872, or some other quantity of fuel.
Entities such as speed, height, and length can only be measured because they don’t exist naturally as indivisible units.
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When most of us discuss computers today, we are referring to digital computers. Digital computers are the ones that help run businesses, manage family budgets, and perform most of the tasks we generally think of as “computer work”.
In fact, digital computers are really what this chapter and indeed this book, is about. As you’ll see later, digital computers convert all programs and their data to strings of 0s and 1s that can be manipulated at electronically fast speeds.
Nonetheless, you’ll probably encounter several analog computers, devices that measure physical phenomena and convert them to numbers, in your lifetime.
For example, a gasoline pump contains an analog computer that measures the amount of gas pumped and converts it into gallon and price amounts that appear on the pump’s register.
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A car has an analog computer that measures drive shaft rotation and converts it into a speedometer reading. A thermometer is an analog computer that measures temperature and converts it into degrees.
2. Central versus Specialized Processors :
Another way to classify computers is according to whether they are the central processors (that is, the CPUs) of their computer systems or specialized processors relegated to dedicated tasks.
Since the circuitry for today’s computers can fit on a tiny silicon chip that costs only a few dollars, all sorts of specialized computers are now liberally embedded into peripheral devices such as keyboards and printers.
In fact, you’ll likely find several specialized computers under the cover of your computer’s system unit. Thus, many computer systems today consist of a hierarchy of processors, with a CPU at the top followed by a set of “slave” chips that perform such chores as helping with keyboard communications or speedily crunching out arithmetic computations. This chapter focuses primarily on the CPU.
3. Full versus Reduced Instruction Set Processors :
Computers must be equipped with a variety of instructions in order to process data effectively. These instructions are called the computer s instruction set. Studies have shown that many computers can be given only a limited number of instructions a fraction of those traditionally provided- and still be able to process data more efficiently.
The remainder of the instructions, while useful, create a certain degree of “overhead” and often only get in the way.
In the mid-1980s, CPUs with limited instruction sets became available. These machines have been aptly named reduced instruction set computers (RISC). Their advocates claim that RISC machines are much faster than their conventional counterparts.
Motorola’s 88000 family of RISC chips, for instance, can process instructions 10 times faster than the 68020 microprocessor, the chip used to power the Macintosh II. Many traditionalists feel, on the other hand, that machines based on RISC technology have a long way to go to prove themselves in the “real” world of business computing.