RISC (Reduced Instruction Set Computer) Explained

What is RISC (Reduced Instruction Set Computer)

What is RISC (Reduced Instruction Set Computer)?

RISC, or Reduced Instruction Set Computer, was developed and launched by IBM in 1980. This is a specific type of architecture that needs fewer instruction sets to function.

Technically, the reduced instruction sets of the architecture allow the processors to run at a higher speed. Ideally, the compilers for the RISC hardware generate various RISC instructions.


  • Reduced Instruction Set Computer is a specific type of processor architecture that operates on much simpler machine instructions.
  • The RISC microprocessors are widely used in smaller devices such as smartphones, tablets, and a lot of electronic devices.
  • The most commonly used RISC processors are the ARM CPUs, but there are lots of others who favor this architecture as well.
  • The simpler and fewer set of instructions of fixed length allow the designers to build better and faster processors.
  • Simple addressing modes and deeper pipelining facilitates fetching, decoding and executing operations along with loading and string in the memory.

Understanding RISC (Reduced Instruction Set Computer)

What is RISC (Reduced Instruction Set Computer)

Reduced Instruction Set Computer refers to those processors that have fewer instructions which help them to operate at a higher speed or perform more MIPS, a short for Millions of Instructions Per Second.

Typically, the concept of RISC has resulted in more thoughtful designs of processors. Some of the most significant design considerations that it has led to are:

  • How well can an instruction of a microprocessor be mapped to the clock speed so that it can be performed in a single clock cycle?
  • How simple the architecture is required and can be made?
  • How much work can the processor do without requiring the help of software?

The answers to these have led to better processors with better designs that have offered higher performance benefits.

It has also offered some other significant benefits related to their design and development. These are:

  • A new processor can be designed and tested much more quickly since it is less complicated
  • The programmers of the applications and operating systems find it easier to develop the codes to use in these processors due to the fewer instruction sets and
  • The space on the processor can be utilized in a much better way and with more freedom, due to the simplicity of RISC.

There are basically five design principles followed in developing an RISC. These are:

  • Single-cycle execution – The design of the most conventional CPUs tend to achieve an optimal execution rate of one instruction in one basic machine cycle. The RISC design emphasizes this particular aspect even at the cost of combining multi-instruction sequences for the less-frequent functions.
  • Hard-wired control – Typically, a microcode adds another layer of explicative overhead, which increases the number of cycles required for each instruction, even if it is the simplest one of all. In RISC design, with little or no microcode and hard-wired control, this issue is also resolved.
  • Simple instructions – Instead of microcode and multi-cycle instructions, fewer addressing modes and simpler instructions are used in RISC design, which keeps things simple and improves the operational speed of the microprocessor.
  • Load and store – In RISC, memory is accessed by loads and stores only, and all others perform register-register activities.
  • Efficient and deep pipelining – With more efficient and deeper pipelining, the efficiency of RISC is enhanced, making more convenient utilization of hardware parallelism.
  • Microcode – There is no complicated horizontal microcode, and therefore it makes the CPU operate faster using the deep pipeline, which keeps a larger number of instructions active at the same time, ideally completing one and starting another.
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Also, the higher-level language compilers can generate more efficient codes in a large number because they now have to use the smaller set of instructions found in a RISC.

Why is RISC Used?

The most significant reason to use RISC is that it offers a much higher and faster performance, increasing its performance per watt ratio, which is typically useful for the devices that run on batteries where energy efficiency is vital.

Some other reasons to use it so extensively include, but are not limited to the following:

  • The RISC processor can carry out a single action in one instruction using only a single cycle to complete it. This optimizes the execution time of each operation.
  • It is very easy to pipeline instructions because it is deep, and, most importantly, the RISC architecture typically uses a preset length of instruction.
  • The architecture supports a larger number of registers because it does not include any complicated instruction decoding logic. This specific aspect reduces the time to load and store values in the memory.
  • Since the designers find it easy to develop RISC processors due to their simplicity and lower number of instruction sets achieved by using smaller components, it reduces the cost per chip.
  • Designing these chips needs fewer transistors due to the reduced instruction sets, which need less chip space.
  • The simple decoding logic allows fitting a larger number of General Purpose Registers or GPRs into the Central Processing Unit.

All these result in increased performance, which is why RISC is considered to be an efficient CPU architecture technology existing today. It is used extensively because it can offer more with less in quick time, and also allows others to do the same.

What are RISC Examples?

One of the most common examples of RISC is the ARM processors, among a host of others, that are used extensively in smaller mobile devices.

Ideally, all modern CPUs use RISC architecture in some way or the other, which is mainly due to the progression of CPU architectures from 8 bits to 16 bits to 32 bits and higher.

Some other examples of processors that have some elements of RISC architecture in them include:

  • The PowerPC
  • The Atmel AVR
  • The MIPS architecture
  • The Microchip PIC
  • The RISC-V
  • The ARC processor
  • The DEC Alpha
  • The Blackfin
  • The AMD Am29000
  • The Intel i860
  • The Intel i960
  • The PA-RISC
  • The LoongArch
  • The Motorola 88000
  • The Power ISA
  • The SuperH
  • The SPARC

What Devices Use RISC?

RISC microprocessors are most commonly used in a variety of electronic devices, including smartphones, laptop computers, desktop computers, gaming consoles, tablets, and a large number of intelligent devices.

Typically, the use of RISC architectures is found on the following platforms.

Low-end, low-power, and low-cost embedded systems, Android based systems, as well as mobile systems such as:

  • The Apple iPhone and iPad
  • Microsoft Windows phone
  • RIM devices
  • Raspberry Pi
  • Nintendo Game Boy Advance and others

The IBM PowerPC is used in gaming consoles such as:

  • Xbox 360
  • GameCube
  • PlayStation 3
  • Wii
  • Wii U

The MIPS line is used in devices such as:

  • Several SGI computers
  • PlayStation, PlayStation 2 and PlayStation Portable game consoles
  • Nintendo 64
  • Residential gateways

Apart from the above, different other variants are used in different devices such as:

  • Hitachi’s SuperH is used in the Saturn, Sega Super 32X, and Dreamcast, which is now developed and sold by Renesas as SH4.
  • Atmel AVR is used in a wide range of products, such as Xbox handheld controllers, BMW cars, and Arduino open-source microcontroller platforms.
  • RISC-V is used for regular and special purpose extensions due to its smaller core integer instruction set, 32-bit or 64-bit address spaces, and compressed ISA for code density.
  • IBM’s PowerPC was used in Apple’s Macintosh computers until 2005 before switching to Intel x86 processors.
  • ARM-based processors in a few Chromebooks, Apple products, the Microsoft Windows Surface line, and HP and Lenovo Windows PCs.
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Several workstations, servers, as well as supercomputers also used different varieties and models of RISC-based microprocessors from the different manufacturers mentioned earlier.

What are the Main Properties of RISC?

The most significant property of the RISC is the fewer number of instruction sets in its architecture. These are much more simplified and smaller, which makes them less complicated.

It also includes register-to-register operations. This means that:

  • All operations are carried out in the registers of the CPU.
  • All data is stored for computation in the processor registers.
  • The results of these operations are transferred using store instructions to the memory.

Some other features of the RISC processor architecture include:

  • Increased number and size of the register set
  • Increased internal parallelism
  • Improved processor average throughput in each cycle
  • Homogeneous instruction format with a single word and the opcode in similar bit positions to allow simple decoding
  • Equal use of all GPRs in all instructions as source or destination
  • Simplified compiler design with the floating-point registers usually kept separate
  • Simpler addressing modes
  • Instruction sequences performing complex addressing
  • Fewer data types in hardware with no Binary Coded Decimal or BCD and byte strings
  • Easy to decode instruction format
  • Fixed and aligned instruction length on word limits
  • Ability to perform one instruction per clock cycle
  • Use of deep pipelining involving fetching, decoding, and executing stages of two or three instructions
  • Less execution time is needed for a program due to the larger number of registers in the CPU
  • Hardwired instead of microcode or micro-program control

Also, the number of addressing modes and transistors committed to the core logic is less due to the simpler addressing of all instructions.

Why is RISC Faster?

Typically, in the Reduced Instruction Set Computer, the instructions are fewer in number, just as its name signifies, which is the primary reason for it to operate at a high speed.

Ideally, every type of instruction that a computer performs needs additional circuitry and transistors.

This additional set of computer instructions makes the processor more complicated, which, in turn, reduces the speed of operation.

In contrast, the RISC processors come with several transistors that increase their speed, which helps them in using the simpler and limited number of instruction sets far more quickly.

This helps in streamlining data processing which accelerates its processing power with the use of a minimum number of instructions stored in the processor permanently.

Is RISC an Operating System?

RISC OS is a computer operating system that typically runs on ARM chipsets. It was designed originally by Acorn Computers Ltd. in Cambridge, England, and was introduced in 1987 to be used in the Archimedes line of personal computers.

Some of the useful features of this operating system are as follows:

  • It is a single-user operating system that uses cooperative multitasking, however, with less comprehensive memory protection.
  • The OS core is stored in the ROM, which offers a faster bootup and keeps it safe from corruption. Later versions are stored in 4 MB of flash memory on an SD card as a ROM image that allows updating without replacing the ROM chip.
  • It is made up of different modules that can be added to, replaced, or soft-loaded through software interrupts.
  • The defined Application Binary Interfaces or ABIs handle the vectors and filters offering several ways for the program to intercept and modify operations and customizing the look and feel by third-party programs.
  • The file system of the operating system is volume-oriented and uses metadata rather than file extensions.
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This operating system is worth using due to its increased usability, which eases the execution of all basic tasks. The features that add to its usability are:

There are a lot of bundled applications in this operating system that help the user get more artistic, allowing the creation of more scalable images, and a popular writer package to handle text and graphics more easily.

Other items included in it are:

  • Calculator
  • Alarm systems
  • Useful tools
  • Third-party software
  • Office applications
  • Music and audio software

Most of the operating areas are better covered in this OS, such as PCloud, which allows easy transferring of files.

You can also use this operating system to program in C, Python, Lua, and a few other languages. However, connectivity support is an issue due to the absence of good web browsers.

All these features make using RISC OS both a pleasure and a struggle. It is not highly likely to replace Windows or Mac completely but is still worth a try due to the pleasant GUI, which is not as interfering or heavyweight as the others.

However, with the development of RISC V, things will surely improve with better hardware support.

Are Intel Chips RISC?

Ideally, Intel x86 does not have a RISC engine but typically uses the x86 instruction set architecture for decoding and execution schemes, mapping the instructions onto machine operations, sequencing them for complex instructions, and finding a way through.

However, Intel joining forces with RISC V CPU Group has raised new speculations. It seems that Intel sees the future in x86, ARM, and RISC-V, all of which will play a major role in the CPU industry.

In fact, Intel has already been making an increasing demand for additional RISC-V chip offerings and Intellectual Property.

In addition to that, Intel has also announced and created a billion-dollar fund to support foundry startups that will prioritize investments in:

  • Chip IP
  • Innovative chip architectures
  • Software tools
  • Advanced packaging technologies

It has also shown initiatives in sponsoring development platforms for open-source software that will cater to all three major chip ISAs.

RISC-V provides open modular building blocks, which help in expanding its ecosystem and drive large-scale commercialization.

In short, Intel is already trying out this game-changer that can become a major chip power in the near future, which is why it has already offered a few RISC-V chips such as the Nios V processors.

Questions & Answers:

Does Windows Use RISC?

Well, several operating systems, including Windows and a few other NixOS flavors have moved to both RISC and CISC.

The Windows 10 IOT, Windows RT, and Windows Phone 7, 8, and 10 also run on RISC hardware.

Is the Apple M1 a RISC Processor?

Yes, the Apple M1 chips are RISC since they are based on the ARM architecture, which itself is a Reduced Instruction Set Computer processor.

Why Does Apple Use RISC?

The main reason that Apple is keen on using RISC is that the architecture provides the designers of processors with simpler and fewer instructions.

It may do less, but it can do it more quickly, adding to the performance improvements.


As you can see from this article, Reduced Instruction Set Architecture is quite useful to enhance the performance level and speed of a processor due to its simple encoding and fixed-length instructions.

The main objective of this design is to simplify the process of fetching, decoding, and issuing logic considerably.

About Taylor

AvatarTaylor S. Irwin is a freelance technology writer with in-depth knowledge about computers. She has an understanding of hardware and technology gained through over 10 years of experience.

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