What is RISC-V?

RISC-V is one of the latest contenders in the CPU field, but what is it and how does it compare to its rivals?

Even for computer geeks, RISC-V is a bit in the weeds, but maybe not for long. It is one of the rising stars in the computing world and is one of the most successful (if not the most successful) examples of open source and open standard hardware. Tens of billions of RISC-V cores are expected to be sold in the coming years, a number that would rival the number of x86 and ARM cores sold in the same time period. Here's everything you need to know about RISC-V and where it's going.

RISC-V (pronounced "risk five") is an instruction set architecture (ISA) developed and maintained by RISC-V International (formerly the RISC-V Foundation). An ISA is the starting point of any CPU design and determines fundamental things like basic instructions, what optional instructions can be added, and what type of software can run natively on the CPU. Additionally, RISC-V is, by name, a reduced instruction set computer architecture, which basically means that its default form comes with very few instructions. ARM is also a RISC design, while x86 is a complex instruction set computer (CISC) design.

Being a RISC design is more important for RISC-V than ARM being RISC or x86 being CISC because RISC-V has a unique selling point: it is an open standard. Any company that wants to use the original RISC-V design is free to do so and modify it however they want. Since x86 is jointly owned by Intel and AMD, no other company can (legally) make x86 processors, and while companies can make their own version of ARM chips, not only do they have to pay Arm, but they can't alter the ES A. With RISC-V, it's total freedom.

Well, maybe not total freedom. Although RISC-V International (the company behind RISC-V) has often billed itself as "open" and "open source," it recently moved away from open source and now talks about RISC-V as an ISA of open standard. This is because actual RISC-V chips can be proprietary and closed source, even though ISA is open source. What you need to know is that while any company or organization can use the RISC-V ISA for free, the actual products may be locked in like x86 or ARM.

Of course, there are advantages and disadvantages to this approach. The good news is that there are no licensing fees or restrictions on designs, which is great for companies that want to be as autonomous as possible and reduce development costs. The bad news is that exercising this amount of freedom is not easy because designing CPUs is not easy. Additionally, companies that make their own RISC-V processors are not required to share that technology with others, but can license designs as Arm does.

A brief history of RISC-V

RISC-V is a strange name. You'd think it's the fifth in a series of RISC ISAs, and while that's the story behind its name, that's not exactly accurate. RISC-I and RISC-II were designed in 1981, but RISC-III and RISC-IV are not real ISAs. Instead, they were names applied to two ISAs called SOAR and SPUR, which came out in 1984 and 1988, respectively. There is no substantial connection between RISC-V and these ISAs from the '80s beyond the fact that they are all RISC designs.

RISC-V is practically a baby among ISAs. Work on RISC-V began in 2010 at the Berkeley Parallel Computing Laboratory (or Par Lab for short), which received funding from Microsoft and Intel, the creator of the x86 ISA. By 2011, the first RISC-V prototype was ready for manufacturing. RISC-V went from a research project to an actual ISA that companies could use in 2014 when David Patterson and Krste Asanović published a paper arguing that open source hardware was the future and that RISC-V was the ISA to do the job. A year later the RISC-V Foundation was created.

It's only been eight years since RISC-V burst onto the scene, and because chip design can take years, it's difficult to assess where RISC-V is right now. What we do know is that there are more than 3,500 members of RISC-V International, up from 600 at the beginning of 2020, 1,500 at the beginning of 2021, and 2,200 at the end of 2021. As for actual market share, it is hard to say, but in May 2023 RISC-V CTO Mark Himelstein stated that member companies had sold "tens of billions" of RISC-V cores, which is in line with predictions for 2022 and 2023 .