Difference Between RISC and CISC processor

RISC vs CISC processor

RISC and CISC are computing systems developed for computers. Difference between RISC and CISC is critical to understanding how a computer follows your instructions. These are commonly misunderstood terms and this article intends to clarify their meanings and concepts behind the two acronyms.

RISC

Pronounced same as RISK, it is an acronym for Reduced Instruction Set Computer. It is a type of microprocessor that has been designed to carry out few instructions at the same time. Till 1980’s hardware manufacturers were trying to build CPU’s that could carry out a large number of instructions at the same instant. But the trend was reversed and manufacturers decided to build computers that were capable of carrying out relatively very few instructions. Instructions being simple and few, CPU’s could execute them quickly. Another advantage of RISC is the use of fewer transistors making them inexpensive to produce.

Features of RISC

– Demands less decoding

– Uniform instruction set

– Identical general purpose registers used in any context

– Simple addressing modes

– Fewer data types in hardware

CISC

CISC stands for Complex Instruction Set Computer. It is actually a CPU which is capable of executing many operations through a single instruction. These basic operations could be loading from memory, carrying out a mathematical operation etc.

Features of CISC

– Complex instructions

– More number of addressing modes

– Highly pipelined

– More data types in hardware

Over the period of time, the terms RISC and CISC have almost become meaningless as both RISC and CISC have undergone evolution and the distinction between the two has progressively become blurred with both being used in computer systems. Many of today’s RISC chips support as many instructions as yesterday’s CISC chips. There are CISC chips using same techniques that were earlier considered to be used for RISC chips only. However, basic differences between the two are easy to comprehend and are as follows.

Talking of differences, RISC puts burden on software makers as they have to write more lines for same tasks. RISC is cheaper than CISC because of fewer transistors required. The speed of the computer is also higher with lesser instructions to follow at the same instant.