RISC vs CISC | difference between RISC and CISC

RISC stands for Reduced Instruction Set Computer architecture, where in emphasis is given on software design. Examples of such architectures are MIPS, SUN Sparc, DEC Alpha, IBM801 etc.

CISC stands for Complex Instruction Set Computer architecture, where in emphasis is given on hardware design. Examples of such architectures are VAX,INTEL x86, IBM 360/IBM 370 etc.


Figure depicts microprocessors of both RISC and CISC types.

RISC will have large program size, while CISC will have small program size.

RISC compiler will be usually complex in design while CISC compiler will be easy in design.

RISC will have single word instruction while CISC will have variable length instruction. RISC support load/store architecture and CISC support memory operands instructions.

RISC do not support indirect addressing mode. Following are the features of RISC vs CISC. Understanding the fundamental differences between RISC and CISC helps in making informed decisions about processor selection and optimization for various computing needs. Let us compare RISC vs CISC and derives difference between RISC and CISC processor types.

Parameters RISC CISC
Full form Reduced Instruction Set Computer Complex Instruction Set Computer
About Instruction set compact, uniform instructions, facilitate pipelining, highly optimized set of instructions Many addressing modes, long instructions, complex set of instructions
Instruction length Fixed Variable
Execution time Each instruction typically takes one clock cycle Instructions can take multiple clock cycles
Pipelining Designed for easy pipelining More challenging to pipeline due to instruction complexity
Memory access Load/Store architecture; separate load and store instructions Instructions can perform multiple operations, including memory access
Decoding Simple Complex
Registers Larger Fewer
Power consumption Generally lower Generally higher
About Source code More lines of code, large memory footprint High code density
About Optimization Allow effective compiler optimization Often require manual optimization of assembly code for embedded systems
Hardware design complexity Simpler More complex
Software programming Requires more instructions to perform complex tasks Can perform complex tasks with single instructions
Compiler design More responsibility on compiler to optimize instruction usage Less responsibility on compiler as instructions are more capable
Examples ARM Cortex-A, MIPS, RISC-V, IBM power systems, SPARC Intel x86, AMD x86, IBM System/360 etc.

Conclusion : The RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures represent two different approaches to CPU design, each with its own strengths and weaknesses. RISC is preferred when efficiency, simplicity, and power consumption are critical factors. CISC is chosen for its ability to handle complex instructions and reduce the number of instructions per program, which can be beneficial for certain computing tasks.

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