Difference between RISC and CISC


RISC: RISC is Reduced Instruction set computer and used simple commands which can be divided into numerous instructions for achieving low-level operation through a single CLK cycle. RISC instructions mainly hold fewer than 100 instructions and utilities fixed instruction format (32 bits). For accessing memory load / store are the main independent instruction.

CISC: CISC is complex instruction set computer and here several Low-level Operations can be performed through single instructions. Low-level operations include load from memory, an arithmetic operation and a memory store or are processed by multistep processes or addressing modes in single instructions.


RISC CISC
1. RISC means Reduced Instruction Set Computer. 1. CISC means Complex Instruction Set Computer.
2. Providing focus on software. 2. Providing focus on hardware.
3. Instruction set size is small in RISC. 3. Instruction set size is large in CISC.
4. Fixed format (32-bits)register based instructions are used in RISC. 4. Variable format ranges (16-64) bits are used per instruction in CISC.
5. In RISC power consumption is lower. 5. In CISC power consumption is higher.
6. Multiple instruction simultaneously execution named pipelining in possible in RISC. 6. Pipelining is not possible in CISC.
7. RISC is basically a microprogramming unit 7. CISC is basically a complex design of compiler.
8. RISC takes more time for execution because instructions are complex. 8. As the instructions are simple, CISC is faster than RISC.
9. Decoding of instructions not easy. 9. Decoding of instructions not easier.
10. Consumes larger disk space. 10. Consumes minimum disk space.
11. Consumes lower power. 11. Consumes high power.
12. Applications, smart phones, PDAS. 12. Applications, Security systems home automation.
13. In RISC, One machine cycle is needed to execute each instruction. 13. In CISC, 2-10 machine cycle are needed to execute each instruction.
14. Hardwired control unit is only used in RISC. 14. Both hardwired and micro programmed control unit are used in CISC.
15. Only register to register arithmetic operations are performed. 15. REG to REG or REG to MEM or MEM to MEM arithmetic operations can be performed.
16. Instruction execution is done in single clock cycle. 16. Instruction execution is done More than one clock cycle.
17. Memory unit is not available and separate hardware is used to implement instructions. 17. Memory unit is available to implement complex instruction.
18. Here, instruction set is reduced. So it has fewer instructions in the instruction set. 18. Variety of instructions can be used in the instruction set for complex operations.
19. Multiple register sets can be used. 19. Only a single register setis used.
20. Code expansion can be considered as a problem. 20. Code expansion is easy and is not a problem.
21. Most commonly used RISC microprocessors are alpha, ARC, ARM, AVR, MIPS, PA-RISC, PIC, Power Architecture and SPARC. 21. Most commonly used CISC Processors are the system/360, VAX, PDP-II, Motorola 68000 family, AMD and intel x86 CPUS.
22. Video processing, telecommunications and image processing related high and operations are used in RISC. 22. Security systems, home automation related low end operations are used in CISC.
23. RISC has separate data and instruction cache design. 23. CLSC has lenified cache for data and instruction.


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Contributed By: Romana Rahman Ema