COMPUTER ARCHITECTURE

RISC and CISC Processors

In this tutorial, we will learn about RISC Processor and CISC Processor and difference between them.


RISC Processor

It is known as Reduced Instruction Set Computer. It is a type of microprocessor that has a limited number of instructions. They can execute their instructions very fast because instructions are very small and simple.

RISC chips require fewer transistors which make them cheaper to design and produce. In RISC, the instruction set contains simple and basic instructions from which more complex instruction can be produced. Most instructions complete in one cycle, which allows the processor to handle many instructions at same time.

In this instructions are register based and data transfer takes place from register to register.


CISC Processor

  • It is known as Complex Instruction Set Computer.
  • It was first developed by Intel.
  • It contains large number of complex instructions.
  • In this instructions are not register based.
  • Instructions cannot be completed in one machine cycle.
  • Data transfer is from memory to memory.
  • Micro programmed control unit is found in CISC.
  • Also they have variable instruction formats.

Difference Between CISC and RISC

Architectural CharactersticsComplex Instruction Set Computer(CISC)Reduced Instruction Set Computer(RISC)
Instruction size and formatLarge set of instructions with variable formats (16-64 bits per instruction).Small set of instructions with fixed format (32 bit).
Data transferMemory to memory.Register to register.
CPU controlMost micro coded using control memory (ROM) but modern CISC use hardwired control.Mostly hardwired without control memory.
Instruction typeNot register based instructions.Register based instructions.
Memory accessMore memory access.Less memory access.
ClocksIncludes multi-clocks.Includes single clock.
Instruction natureInstructions are complex.Instructions are reduced and simple.