Difference Between RISC and CISC
Contents
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.
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
- 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