Difference Between RISC and CISC
Comparison between RISC and CISC
The Major Difference Between RISC and CISC is that 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.
|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
- Relatively few instructions.
- Relatively few addressing modes.
- Memory access is limited to load and store instructions.
- All operations are done within the registers of the CPU.
- Fixed-length, easily decoded instruction format.
- Single-cycle instruction execution.
- Hardwired rather than microprogrammed control.
- A relatively large number of registers in the processor unit.
- Use of overlapped register windows to speed-up procedure call and return.
- Efficient instruction pipeline.
- Compiler support for efficient translation of high-level language programs into machine language programs.
Characteristics of CISC
- A larger number of instructions – typically from 100 to 250 instructions
- Some instructions that perform specialized tasks and are used infrequently
- A large variety of addressing modes – typically from 5 to 20 different modes
- Variable-length instruction formats
- Instructions that manipulate operands in memory