Intel and AMD are focused on the x86(-64) ISA, with a strong presence in the desktop and server space [1]. ARM is everywhere mobile, they really cornered the "

Intel and AMD are focused on the x86(-64) ISA, with a strong presence in the desktop and server space [1]. ARM is everywhere mobile, they really cornered the "low-power" (ie energy) space way ahead of Intel and AMD. They provide a great ecosystem of IPs and tools around them. Think of them as the "battery's included" DIY provider for building chips. But both of the above generally target general-purpose CPUs [2], the one you usually think as being the core of your computer. But there are others! DSPs have dedicated instructions for saturated math (no overflow/rollover) and multiply-accumulate, GPUs are DSPs on steroids, and there's otherwise an entire spectrum of complexity you can have from your 8-bit integer microcontroller that doesn't even have a divide instruction, all the way up to the massively-parallel floating-point processors. Problem is, that spectrum was divided between many different proprietary ISAs, each with their various levels of tool sophistication and support. RISC-V is based on the idea that we can do a better job unifying the ISAs across this spectrum of processor complexity. It's an extensible ISA that starts with basic integer-only operations and direct addressing, and can extend with instructions for more sophisticated operations such as adding 32-bit floating operations, 64-bit float, supervisor mode, hypervisor mode, SIMD... All of which can share a common ecosystem of compilers, formal verification, debuggers... But the real popularity of RISC-V is that you can use its ISA, and design a chip around it, freely without having to pay a (expensive!) license to ARM. This does present an existential threat to ARM, although they have a strong head-start in offering a ready-made ecosystem of tools. Do you want to spend $10M in engineering manpower and experimental silicon tape-out designing your new chip? Or just pay $2M to ARM to license their known-good CPU? It takes a lot of effort, expertise (and iteration!) to design a CPU core that's as performant and feature-full as what ARM spent years (decades!) perfecting. Do companies choose RISC-V because it allows them to re-use their tools on novel chip designs, or because it's just cheaper and, new as it is, sufficient for their purposes? It's exciting to watch the development. (Also I can't help but notice that many of the RISC-V chip announcements are coming from China) [1] Fun fact: in the 80s and 90s, x86 was the "cheap, consumer" chip that was looked down upon by the Workstation class RISC-type chips like the Sun Sparc, or DEC Alpha (and much of Apple's chip design team sprang from a core of ex-DEC designers!) But Linux came along, Intel kept improving their chips, and took over the workstation/big-iron space from the incumbents [2] cue the corrections about ARM's (and Intel's!) GPU design, co-processor architecture...