RISC Vs CISC: Which is Better?

RISC Vs CISC: Which is Better?

Many people nowadays believe that the difference between RISC and CISC computer processors is insignificant and that their performance is practically the same. Is this true? The fact is that there are still significant distinctions between both, which might make one better suited to particular applications than the other. In this post, we’ll go over some of the fundamentals of microprocessors before diving into the more complex issues of RISC vs. CISC. The objective of both RISC and CISC designs is to improve CPU performance, although they go about it in different ways. Many people consider RISC to be an improvement over CISC. The argument for RISC over CISC is that having a simpler set of instructions makes developing a CPU easier, less expensive, and faster.

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What is RISC?

RISC stands for Reduced Instruction Set Computer Processor, a microprocessor architecture having a minimal set of instructions that may be greatly modified. It is designed to reduce instruction execution time by optimizing and restricting the number of instructions. It means that each instruction cycle takes just one clock cycle and has three parameters: fetch, decode, and execute. The RISC processor can also perform complicated instructions by breaking them down into smaller ones. RISC devices need several transistors, which makes them less expensive to develop and reduces instruction execution time.

What is CISC?

CISC stands for Complex Instruction Set Computer. It has a huge number of sophisticated instructions ranging from simple to highly complex and specialized on the assembly language level, which takes a long time to execute. As a result, CISC addresses each program by lowering the number of instructions while ignoring the number of cycles per instruction. It underlines the need of writing complicated instructions directly in hardware since the hardware is always quicker than software. CISC chips, on the other hand, are slower than RISC CPUs but use fewer instructions. VAX, AMD, Intel x86, and the System/360 are examples of CISC processors.

Architecture- RISC vs CISC:

  • The core idea behind RISC is to simplify hardware by employing an instruction set consisting of a few basic stages for loading, evaluating, and saving operations. For example, a load command will load data, while a store command will save data.

The basic notion for CISC is that a single instruction will do all loading, evaluating, and storing operations, similar to how a multiplication command will perform loading, evaluating, and storing operations; hence, it is complex.

  • Both techniques aim to boost CPU performance.
  • Previously, when programming was done in assembly, there was a need to make instructions do more tasks because programming in assembly was tedious and error-prone, which led to the evolution of CISC architecture, but with the rise of high-level language dependency on assembly reduced, RISC architecture prevailed.

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Example- RISC vs CISC:

Let’s say we need to add two 8-bit numbers: CISC approach: For this, there will be a single command or instruction, such as ADD, that will complete the task. RISC approach: In this approach, the programmer will write the first load command to load data into registers, then use a suitable operator, and finally store the result in the desired location. As a result of the division of the add operation into parts, namely load, operate, and store, RISC programs are longer and require more memory to be stored, but require fewer transistors due to the less complex command.

Major Distinctions Between CISC and RISC

The major distinction between RISC architecture and CISC architecture is that RISC-based machines execute one instruction every clock cycle. Each instruction in a CISC processor performs so many activities that it takes many clock cycles to execute. Every instruction in a RISC processor has a set memory size, making it easy to decode and execute. Instructions on a CISC system might have different lengths, which increases processing time. 

RISC Vs CISC:

 

RISC CISC
is a reduced instruction set computer. It is a Complex Instruction Set computer.
It places a premium on software to optimize the instruction set. It places a premium on hardware to optimize the instruction set.
It is a hardwired programming unit in the RISC Processor. It is a microprogramming unit in a CISC processor.
The instruction must be stored in various register sets.  To save the instruction, a single register set is required.
Instruction decoding is straightforward in RISC. Instruction decoding is complicated in CISC.
In RISC, pipeline applications are straightforward.  Pipeline applications are tough to find in CISC.

 

Which is better: RISC vs. CISC?

The quick answer is that no architecture is superior to another. Each has advantages and disadvantages that make them better suited to specific settings. The goal is to match those benefits and drawbacks with the planned application to determine the best instruction set architecture for you. If you want to know more about such technical topics related to VLSI, Chipedge has got you covered. It is one of the best VLSI training institutes in Bangalore that offers a wide range of VLSI design courses and much more. Get in touch with us today!

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