RISC and CISC Architectures, Differences, Advantages and Disadvantages

RISC and CISC Architectures, Differences, Advantages and Disadvantages


[What is RISC & CISC?]

RISC is an abbreviation for Reduced Instruction Set Computer while CISC is the abbreviation for Complex Instruction Set Computer. Both are architectures that form the basis of building processors.

An Instruction Set is the hard-coded operations that can be performed at the CPU hardware level. A CPU cannot perform any operations outside its instruction set. We have two ways to create instruction sets, that is, RISC or CISC. These two differ in several ways.

RISC processors use simplified instructions that execute at a high speed while CISC processors use sophisticated instructions that can perform multi-step low-level operations but that execute comparatively at a lower speed.

[RISC and CISC differences]

1. RISC is Reduced Instruction Set Computer while CISC is Complex Instruction Set Computer.
2. RISC takes simple, standardized instructions while CISC takes sophisticated instructions that can vary in length.
3. RISC can use several simple instructions to perform an operation while CISC can use one sophisticated instruction to perform multi-step operations.
3. RISC relies heavily on software while CISC heavily depends on hardware.
4. RISC can only support limited addressing modes while CISC can support compound modes of addressing.
5. RISC uses single-clock cycle while CISC uses multi-clock cycles.


[RISC Advantages & Disadvantages]

[Advantages of RISC]

1. Reduced instruction sets results in better processor performance.
2. RISC instructions are simple and thus do not require microcode to translate them.
3. It is cheaper as it requires few transistors to make.
4. Implementing pipelining is easy and makes RISC processors efficient.


[Disadvantages of RISC]

1. If a subsequent instruction depends on preceding instructions, RISC can be slow.
2. The access speed of the memory compared to the processing speed of the CPU makes processing many instructions slow for RISC, which is it’s bottleneck.
3. More lines of code are used in RISC, thus implying more work by the programmers and compilers.


[CISC Advantages & Disadvantages]

[Advantages of CISC]

1. Uses less lines of code as many instructions can be included in one line.
2. Uses less memory as the length of code is generally short.
3. Dependency on hardware makes CISC efficient when processing multiple interdependent instructions.
4. CISC processors creates a process to manage and adjust the clock speeds.
5. Less effort is required by compilers to translate instructions.


[Disadvantages of CISC]

1. CISC are less efficient in executing single instructions per cycle.
2. Implementation of pipelining in CISC is difficult, and also complicated to utilize.
3. CISC requires more transistors to make, making them more expensive.


RISC and CISC Architectures, Differences, Advantages and Disadvantages
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