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Difference between RISC and CISC - RISC vs CISC

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Difference between RISC and CISC - RISC vs CISC

RISC and CISC are two popular forms of computer architecture that find extensive use in computing. This means that both RISC and CISC define the characteristics of the set of commands used to program your device. However, they are vastly different in terms of complexity, data formats, modes of address, registers, flow control mechanisms, and, opcode specifications etc.

What is RISC?

Reduced Instruction Set Computing or RISC is a form of microprocessor architecture that uses a set of simple commands that are divided into numerous instructions. With one CLK cycle, this architecture can achieve a low-level operation. This increases the device’s power efficiency and makes it extremely useful for use in portable devices.

Architecture of RISC

This CPU design works on the principle of quick actions through a condensed set of instructions. Every instruction completes a small task that results in the successful compilation of complex commands quickly in a single cycle. The lengths and formats of the instructions are kept similar to each other.

Applications of RISC

High-end applications such as telecommunication, video processing, and image processing use RISC. This is a result of the quick response time and power efficacy.

What is CISC?

Complex Instruction Set Computing or CISC uses a single instruction that can carry out several operations. These are usually low-level operations like an arithmetic operation. The various memory reference operations use a large number of addressing modes. As a result, CISC uses a variable format. This actually saves the space required to store the memory and consequentially the memory cost.

Architecture of CISC

The CPU design in CISC architecture uses a single command that executes various operations in several steps. These compound instructions are executed fully in two to ten cycles and thus require a longer execution time. The CISC architecture works with the HLL statements in the firmware and uses a common path and cache for both data and instruction.

Applications of CISC

CISC architecture usually finds application in low-end applications such as security systems, home automation, etc.

Key Differences Between RISC vs CISC

Here is a list of difference that will help you evaluate RISC vs. CISC.



Simple instructions carried out in a single cycle.

Complex instructions take numerous cycles for execution.

Average clock cycle per instruction is 1.5.

Average clock cycle per instruction is 2-15.

More focus on software to optimise performance.

More focus on hardware to optimise performance.

No memory unit but distinct hardware to implement instructions.

Memory unit needed to implement instructions.

Hard-wired unit of programming

Microprogramming unit

Uses multiple registers

Uses a single register

The processor is vastly pipelined.

The processor is less pipelined.

Code expansion is problematic.

Code expansion is not problematic.

Instruction decoding is simple.

Instruction decoding is complex.

A fixed format for instructions.

The format for instructions is not fixed.

Therefore, it is evident that RISC holds more advantages over CISC when it comes to designing computer architecture for high-end operations. It deals with large sets of information more rapidly and in a pipelined manner. However, it proves more expensive in terms of memory storage than CISC. This clearly elucidates that both RISC and CISC has advantages and disadvantages and you should decide on which to use keeping in mind the end application.