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Difference between RISC and CISC Architectre in Microprocessor

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Difference between RISC and CISC Architectre in Microprocessor


There are two major types of CPUs, which are classified according to the instruction set philosophy adopted by their designers. They are.

a.  CISC (Complex Instruction Set Computer).

b. RISC (Reduced Instruction Set Computer).

Let us discuss both of them in detail.

   a.   CISC (Complex Instruction Set Computer).

The instructions which the processor could execute were built into the chip. In common CISC Chips are relatively slow per instruction. Therefore CISC has a large amount of different and complex instructions(i.e this architecture do very complex and difficult instructions).CISC architecture was a bit complex because of the instructions used at the hardware level. The more complex the instruction set, the greater the overhead of decoding an instruction. CISC emphasizes on hardware So we discuss some examples. Examples of CISC processors is the Motorola 680×0 families and intel 486 and Pentium series.

b. RISC(Reduced Instruction Set Computer).

Reduced Instruction Set Computer (RISC)is a microprocessor architecture that is designed to perform a smaller number of instructions and RISC architecture was developed around id 1980 ad reaction to the CISC chips, therefore It is designed to perform a smaller number of instructions in order to operate at a higher speed. RISC has limited and simple instruction set. The simplicity of RISC allows more freedom to choose how to use the space on a microprocessor.

The larger set of instructions make the microprocessor more complicated and slower in operation. Operating System and application programmers will find it easier to work with the smaller instruction set.


One of the drawbacks of the RISC is that it puts a lot of burden on software dude to its smaller size of an instruction set. RISC emphasized on software. Examples of RISC processor are IBM PowerPC, Sun SPARC and some mobiles.

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