RISC and CISC Processors

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 Characterstics Complex Instruction Set Computer(CISC) Reduced Instruction Set Computer(RISC)
Instruction size and format Large set of instructions with variable formats (16-64 bits per instruction). Small set of instructions with fixed format (32 bit).
Data transfer Memory to memory. Register to register.
CPU control Most micro coded using control memory (ROM) but modern CISC use hardwired control. Mostly hardwired without control memory.
Instruction type Not register based instructions. Register based instructions.
Memory access More memory access. Less memory access.
Clocks Includes multi-clocks. Includes single clock.
Instruction nature Instructions are complex. Instructions are reduced and simple.

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