Difference Between RISC and CISC

Difference Between RISC and CISC in Tabular Form

Difference Between Reduced Instruction Set Computers(RISC) and Complex Instruction Set Computers(CISC)

RISC and CISC are the computer instruction sets which is a part of computer architecture. The Key Difference Between RISC and CISC is in the number of computing cycles each of their instructions take.

Comparison Chart

RISC CISC
RISC stands for Reduced Instruction Set Computer CISC stands for Complex Instruction Set Computer.
It has fewer instructions It has more instructions
Less addressing modes. More addressing modes.
RISC requires more RAM CISC requires a minimum amount of RAM
The average Clock cycles Per Instruction(CPI) of a RISC processor is 1.5 The average Clock cycles Per Instruction of a CISC processor is between 2 and 15
Small Code Size. Large Code Size.
RISC processors have a fixed instruction format CISC processors have variable instruction format.
Multiple register sets are present Single register set
RISC processors are highly pipelined. CISC processors are not highly pipelined or less pipelined.
Low power consumption. High power consumption
Focus on software to optimize performance. Focus on hardware to optimize performance.
Uses multiple registers Uses a single register
Compound addressing mode. Limited addressing mode.
RISC microprocessors are Alpha, ARC, ARM, AVR, MIPS, PA-RISC, PIC, Power Architecture, and SPARC. CISC processors are the System/360, VAX, PDP-11, Motorola 68000 family, AMD, and Intel x86 CPUs.

Characteristics of RISC

  1. Relatively few instructions.
  2. Relatively few addressing modes.
  3. Memory access limited to load and store instructions.
  4. All operations are done within the registers of the CPU.
  5. Fixed-length, easily decoded instruction format.
  6. Single-cycle instruction execution.
  7. Hardwired rather than microprogrammed control.
  8. A relatively large number of registers in the processor unit.
  9. Use of overlapped register windows to speed-up procedure call and return.
  10. Efficient instruction pipeline.
  11. Compiler support for efficient translation of high-level language programs into machine language programs.

Characteristics of CISC

  1. A larger number of instructions – typically from 100 to 250 instructions
  2. Some instructions that perform specialized tasks and are used infrequently
  3. A large variety of addressing modes – typically from 5 to 20 different modes
  4. Variable-length instruction formats
  5. Instructions that manipulate operands in memory

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