Risc v. Cisc
There are two very general types of processor in use - risc, Reduced Instruction Set Computers and cisc, Complex Instruction Set Computers. Processors such as the 386 family are cisc processors. They have a large and powerful set of instructions which programs can use. For example the 386 can perform a multiplication or division in a single instruction where many other processors take tens of instructions to do the same task.
It is difficult to see how there could be any alternative to the progression of increasingly powerful cisc processors. The philosophy of risc design, however, is that a complex instruction set is difficult to implement efficiently and most of the time programs only use 10% or fewer of the available range of instructions. Instead of trying to implement a full cisc instruction set efficiently, the risc approach is to concentrate on just the 10% of the instructions that are used often. The resulting processors have a small but very fast instruction set. Risc processors have proved that they can match and surpass the performance of cisc chips such as the 386 while being much simpler and cheaper to build.
The future of the risc versus cisc argument is difficult to predict. It is likely that PCs based on risc designs will become more common as 386 software such as Windows NT is designed to also run on risc processors. However, a more subtle effect of the rise philosophy is on the future generation of cisc chips. The 486, for example, gains much of its speed by optimizing the speed of the most commonly used instructions. This is of course exactly the principle used in designing a risc processor! It is going too far to say that the 486 is a cross between a cisc and a risc processor but it weakens the argument that to reach increased processing power we have to move to risc at the expense of cisc.
average
measure of performance but your applications may be very specific in their use
of a processor’s instruction set. The result is that it can be difficult to
predict how much effect an improvement in the MIPS rating will have on the
speed of your particular application.
The
first desktop computers offered performances below O.5MIPS. Today’s 386/486
based systems offer performances in the region of 1OMIPS. At these levels of
performance desktop computers can be used for tasks that traditionally needed a
mainframe or a workstation such as real time solid modelling, animation and
complex equation solving.
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