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Although their names are very similar, there are a lot of things to distinguish RISC and CISC from each other. Both are rather abstract concepts and refer to a type of computer architecture by which the processor performs its operations.

But there are strengths and weaknesses to both, depending on the application they’re used for, and fundamental differences in the way that they work. With that said, let’s explore what sets these architectures apart in our RISC vs CISC comparison.

RISC vs CISC: Side-by-Side Comparison

RISCCISC
NameReduced Instruction Set ComputerComplex Instruction Set Computer
What it isComputer architectureComputer architecture
How it’s usedFor generalized, simple, standardized instructions, as well as pipelining (often used in video and image editing)For complex and less general instructions. (often used in automation devices and security)
Instruction sizeSingle wordLarger than one word
EmphasisSoftwareHardware
RAM useHeavyMore efficient
Cycles per instructionOneMany

RISC vs CISC: What’s the Difference?

It’s important to know the differences between RISC and CISC, particularly if you’re a programmer or developer. Have a closer look at these distinctions below.

What They Are

Both CISC and RISC can be thought of as different designs for the architecture, or structure, of a processor, usually the CPU. As such, RISC and CISC are known as ISAs or Instruction Set Architectures.

Essentially, the CPU tells the computer what functions to carry out, and it does this by reading a set of instructions. The way that these instructions are communicated with the CPU is determined by the architecture.

Development

rtx
CISC involves single instructions executing several low-level operations (such as a load from memory).

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To put it simply, CISC is the predecessor to RISC and was developed earlier in the 1970s, when microprocessors were introduced. You’ve probably heard of the most common CISC family – the x86 architecture developed by Intel.

CISC was very suitable for most applications at the time, as processors and programs were relatively simple by today’s standards. As computers rapidly became more complex, the redesigned RISC came into play in 1980, which was developed by IBM.

It took a while before RISC was widely used, mostly due to a lack of software that was compatible with the architecture. But nowadays, RISC is mostly seen as the superior architecture and is ubiquitous; found in PCs and mobile devices.

How They Work

The main idea behind CISC processors is that a single instruction can be used to do all of the loading, evaluating, and storing operations. Because of this, instructions are relatively more complicated compared to RISC, hence the name Complex Instruction.

This is actually a retroactive definition, introduced once RISC was developed. CISC computers tend to have smaller programs with larger sets of instructions. Because of this, CISC uses a lesser number of instruction sets than RISC to execute the same command.

On the other hand, the concept of RISC is to reduce the complexity of instructions by increasing the number of instructions but reducing the size of the sets. In this way, commands are simplified, and low-level operations are easier to achieve since instructions can be executed faster.

Instructions are reduced to one-word commands. This simplification gives the name Reduced Instruction Set. RISC often gives a speedier performance due to its pipelining capabilities. This means that, generally, operations are carried out in less time because the CPU can work on executing the next operation before the current one is completed.

Cycles Per Instruction

Since the CISC approach works to reduce the number of instructions per program, this generally has a detrimental effect on the processing speed. This is because fewer operations can be completed per clock cycle, as each operation has a more expansive and complex instruction set. Therefore, executing these instructions takes longer than a clock cycle.

Powerful workstation chips
The key operational concept of the RISC computer is that each instruction performs only one function, increasing the speed.

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In contrast, RISC aims to simplify these operations. As the instructions are simplified and spread out, the computer can carry out one instruction per clock cycle. This does, however, increase the number of instructions per program, as each instruction is simpler.

RAM Required

In general, RISC is more dependent on RAM than CISC. This is mostly because the code length in CISC is drastically shorter, and also because RISC relies on pipelining instructions and more complex lines of code.

As such, more RAM is required to simultaneously work on these operations. RAM capacity has greatly increased over time, but so has the demand for it due to the prevalence of RISC architecture.

Bottleneck

Since the goals and uses of RISC and CISC are different, practically, they result in different limitations to performance. RISC implies more pressure to design efficient software with simplified instructions, as RISC relies on this to carry out its tasks effectively.

On the other hand, CISC shines where complex instructions are required, so hardware changes, such as increasing the number of transistors, help to implement a greater number of more complex instructions.

Applications

Common CISC processors are AMD, VAX, and Intel x86. CISC is more commonly used in applications like automation within the home, as well as security devices, whereas RISC is more likely to be found in mobile devices and handheld gaming consoles.

However, in reality, when one is used, the other is used as well. Most computer systems use a mix of CISC and RISC architecture to carry out their functions efficiently.

RISC vs CISC: 8 Must-Know Facts

  1. RISC stands for Reduced Instruction Set Computer, and CISC stands for Complex Instruction Set Computer.
  2. RISC tends to give better performance in most cases, as well as improved energy efficiency.
  3. CISC is more appropriate for complex instruction tasks, such as programming.
  4. RISC uses a larger number of simpler instruction sets, whereas CISC uses a smaller number of more complex instruction sets.
  5. RISC is more dependent on RAM than CISC.
  6. CISC was retroactively named Complex after RISC was developed.
  7. RISC can complete one instruction per clock cycle, whereas CISC will take more than one cycle for the same instruction.
  8. Most modern PCs and mobile devices use a combination of RISC and CISC.

RISC vs CISC: Which One Is Better? Which One Should You Choose?

Strictly speaking, no one architecture can be considered better than the other. Both types of architecture aim to increase CPU performance; they just differ in their approach.

While CISC tries to do this by reducing the number of operations, RISC does it by simplifying instructions and carrying out more of them per clock cycle. In reality, most modern computer systems will utilize a mixed architecture to perform various tasks. 

In general, RISC is seen as an improvement over CISC. This is mostly because it’s cheaper due to fewer transistors required, its simpler design, as well as its tendency to perform quicker. RISC tends to be more power efficient also.

A case where RISC is not superior, however, is when it comes to programming and compiling. These jobs more often than not use complex instructions, so they’re better suited for CISC. RISC is also a lot more dependent on RAM capacity than CISC, because subsequent instructions may depend on the completion of previous instructions.

In most cases, you won’t have much choice in using one over the other. But if you’re a programmer or developer, you’ll likely be using CISC more often. In most other cases, RISC tends to be the more efficient of the two.

Up Next

RISC vs CISC: 7 Differences Explained FAQs (Frequently Asked Questions) 

What do RISC and CISC stand for?

RISC stands for Reduced Instruction Set Computer. CISC stands for Complex Instruction Set Computer.

What are RISC and CISC?

RISC and CISC are types of computer architecture, meaning the way the processor is structured. They determine the form in which instructions are delivered to the CPU, and how it carries out these operations.

What's better, RISC or CISC?

Generally, RISC is seen as the superior architecture, with faster performance and lower energy consumption. However, the situation isn’t always clear-cut, as some situations, such as programming and compiling, rely more heavily on complex instructions. This is where CISC is preferable.

Which is cheaper, RISC or CISC?

Generally, RISC is the cheaper architecture, due to the simpler design and lower number of required transistors.

Is RISC or CISC more dependent on RAM?

Because RISC relies on pipelining instructions to improve performance and more complex lines of code, it’s more heavily dependent on RAM capacity to load, save and carry out instructions simultaneously.

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