Pronounced
risk, acronym for
reduced instruction set computer, a type of
microprocessor that recognizes a relatively limited number of
instructions. Until the mid-1980s, the tendency among
computer manufacturers was to build increasingly complex
CPUs that had ever-larger sets of instructions. At that time, however, a number of computer manufacturers decided to reverse this trend by building CPUs capable of
executing only a very limited set of instructions. One advantage of reduced instruction set computers is that they can execute their instructions very fast because the instructions are so simple. Another, perhaps more important advantage, is that RISC
chips require fewer
transistors, which makes them cheaper to design and produce. Since the emergence of RISC computers, conventional computers have been referred to as
CISCs (complex instruction set computers).
There is still considerable controversy among experts about the ultimate value of RISC architectures. Its proponents argue that RISC machines are both cheaper and faster, and are therefore the machines of the future. Skeptics note that by making the hardware simpler, RISC architectures put a greater burden on the software. They argue that this is not worth the trouble because conventional microprocessors are becoming increasingly fast and cheap anyway.
To some extent, the argument is becoming moot because CISC and RISC implementations are becoming more and more alike. Many of today's RISC chips support as many instructions as yesterday's CISC chips. And today's CISC chips use many techniques formerly associated with RISC chips.
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