Today, many people say that the difference between RISC and CISC computer processors is negligible and that their performance is essentially the same. But is that really true? The reality is that there are still plenty of differences between them and that can make one better suited to the other to certain applications.
In this post, we’ll take a look at some of the basics of microprocessors before delving into the deeper questions about RISC vs. CISC.
What is a microprocessor?
RISC and CISC are both examples of different designs for computer microprocessors. The microprocessor, known as the central processing unit (CPU), is the brain of the computer. It reads instructions from memory that tells the computer what to do. Microprocessors use those instructions to perform very simple tasks, such as basic logic, controlling and input/output operations that are specified by the makers of the operating system.
RISC, which is an acronym for Reduced Instruction Set Computer, and CISC, short for Complex Instruction Set Computer, refer to the category of the processor, or more accurately, the instruction set architecture (ISA). The ISA is the particular way the processor communicates with the human programmer. The earliest computers had a CISC architecture, but in the 1980s, RISC architecture was developed to overcome the increasing complexity of CISC processors.
The CISC approach
The main idea behind CISC processors is that a single instruction can be used to do all of the loading, evaluating and storing operations. The goal of the CISC approach is to minimise the number of instructions per programme. However, that increases the number of cycles per instruction.
The RISC approach
The primary goal of RISC processors is to make hardware simpler by using an instruction set that’s composed of a few basic steps for loading, evaluating and storing operations. It’s not necessarily about having fewer instructions, it’s more about how those instructions are used. That reduces the number of cycles per instruction but comes at the cost of increasing the number of instructions per program.
What are the differences between RISC and CISC?
The purpose of both RISC and CISC architectures is to increase CPU performance, but they try to achieve that goal in different ways. Generally speaking, RISC is seen by many as an improvement over CISC. The argument for RISC over CISC is that having a less complicated set of instructions makes designing a CPU easier, cheaper and quicker.
The primary difference between RISC and CISC architecture is that RISC-based machines execute one instruction per clock cycle. In a CISC processor, each instruction performs so many actions that it takes several clock cycles to complete. In a RISC processor, every instruction also has a fixed memory size, which makes them easier to decode and execute. In a CISC machine, the instructions can be variable lengths, which increases the processing time.
At a glance, the main differences between RISC and CISC architecture are as follows:
Emphasis on software
Emphasis on hardware
Small number of fixed length instructions
Large number of instructions
Simple, standardised instructions
Complex, variable-length instructions
Single clock cycle instructions
Instructions can take several clock cycles
Heavy use of RAM
More efficient use of RAM
Low cycles per second with large code sizes
Small code sizes with high cycles per second
What is RISC-V?
Now we have an understanding of the differences between RISC and CISC architecture, let’s complicate things by introducing RISC-V. The electronics industry seems to have gone crazy for RISC-V (pronounced ‘risk-five’), but why?
RISC-V, like RISC and CISC, is an instruction set architecture (ISA). However, it is an open and free ISA. That means anyone can contribute to its development and it doesn’t cost a penny to use. This is significant because it allows smaller device manufacturers to build hardware without having to pay royalties.
RICS-V has been designed to have a small, fixed-based ISA along with modular, fixed standard extensions that work well with the majority of code. That leaves plenty of room for application-specific extensions to create custom processors for specific workloads.
The benefits of RICS-V over conventional RICS and CISC architecture include:
1. Flexibility - The ability to customise the processor allows engineers to configure chipsets to be big, small, powerful or lightweight, depending on the specific requirements of a device.
2. Innovation - Companies can implement the minimal instruction set and use custom extensions and defined extensions to create processors for cutting-edge tools.
3. Reduced costs and faster to market - The reuse of open-source intellectual property helps to reduce the cost of development and enables companies to get their design to market more quickly.
RISC vs. CISC vs. RISC V: Which is better?
The short answer is that no one architecture is better than the others. Each has its benefits and roadblocks, which make them better suited to particular scenarios. The key is to match up those advantages and roadblocks with the intended application to find the most appropriate instruction set architecture for you.
31 Jan 2021
State of the Power Electronics Recruitment Market for Design and Sales
After a COVID-sized slump, the power electronics recruitment market for design and sales roles is now recovering. If you’re looking for a talented power electronics professional, our unique insights will show you why now could be a great time to hire.
18 Jan 2021
State of the Power Electronics Jobs Market for Design and Sales
It’s fair to say that the power electronics jobs market has been on a bit of a bumpy road over the last six months. However, if you’re looking for a new role in power electronics sales or design, the good news that the jobs market has bounced back. Demand is now on the up, with employers increasingly looking for candidates with design-in wins.
22 Dec 2020
At PER-International, the COVID-19 hiatus is over and we’re officially back to doing what we do best - connecting the world’s best electronics, power electronics, SMPS, UPS and semiconductor professionals with leading employers around the world.
09 Mar 2020
What is the impact of the coronavirus on the global supply chain?
The coronavirus outbreak has had a significant impact on the global supply chain, but when will it peak and how is it affecting businesses around the world?
24 Jan 2020
How to get a non-EEA visa to work in the UK electronics industry
Calling all migrant electrical engineers – the UK needs you. But how can non-EEA electrical engineers tap into opportunities in the UK electronics industry?
12 Dec 2019
Rapid growth creates skills shortages in the UK electronics sector
The UK electronics sector experienced the fastest rate of growth of any manufacturing sector last year, but a shortage of skilled workers threatens to stop the industry in its tracks.
13 Nov 2019
Electrical engineers are added to the UK’s shortage occupation list
PER-International is happy to report that recent changes to the UK’s visa policy mean that electrical engineers and electronics engineers have now been added to the Shortage Occupation List.
13 Sep 2019
US-China trade war reroutes global electronics supply chains
Global electronics supply chains are being rerouted as a result of the continuing trade war between the US and China. However, it’s the US importers who are being left to pick up the bill.
09 Jul 2019
London’s eco-city aspirations and the role of electric vehicles
With Sadiq Kahn’s ULEZ initiative and the Electric Vehicle Taskforce, we’re being prepped for a fully electrified London. What can we expect and when?
09 Jul 2019
The UK seeks middle ground in Huawei 5G dispute
The UK’s decision not to call for a blanket Huawei ban is its way of securing the network against interference while ensuring its 5G networks are competitive.
29 May 2019
The impact of working from home on employee mental health
The benefits of home working for employee mental health are often cited, but could there also be a damaging side to the flexible working revolution?
29 Apr 2019
Is it time to fundamentally rethink workplace culture?
Have you ever wondered whether there might be something fundamentally wrong with workplace culture? No? What if we told you that research has found that around the world, just 13 percent of employees are engaged…