: How did ARM become so popular over other RISC architectures


ARM has been increasing its foothold of the SoC space since the appearance of early smartphones, and we can now see ARM cores used even in the personal computer to cloud computing space.

while there are many open source RISC architectures, ARM is still very popular and growing. what makes it such a popular architecture over other RISC architectures?

In: Engineering

Its not as simple as having an instruction set, you aren’t going to get anywhere with an open source instruction set if no one is making your chips to sell.

People continue using ARM cores these days because ARM is heavily documented and widely supported from compilers to software. Switching instruction sets, particularly to a completely new one with no support, comes with massive tech debt.

People originally used ARM because ARM was available, the ARM corporation sold its own chips and was willing to work with manufacturers, ARM soon partnered with Apple and was found some success there, though Apple was still in its slump (but Apple having a part in ARM’s creation would come back to benefit them). ARM was one of the first RISC instruction sets created, had CPUs sold by the company afterwards, and found its way into most phones even before the original iphone.

I would say the business model is a huge factor. If you want a custom SoC, ARM is a cheap way to do it. ARM sells an IP core (think the design), so you can configure and add stuff, and then send that off to a chip factory to make an SoC.

ARM runs Linux well, it’s got good performance, and unlike x86, you can get the chip customized.

a lot of it is licensing

x86 is too closed. only intel/amd can design new chips, so you’re stuck with whatever they make. because intel/amd have been in an arms race of performance they neglected efficiency so x86 is bad for phones. there have been x86 phones but their battery life was terrible

openRISC is too open. anyone can make their own purpose-built chips, but you have to share whatever design you come up with. that alone makes them a non-option for companies that feel compelled to hoard their “trade secrets”

ARM is a goldilocks zone for these companies. they give just about any company lots of freedom to design their own chips and little requirement to share anything. there are low-power ARM systems that barely use any electricity at all, and there’s apple’s M1 that competes with high-end x86 CPUs

of course there are other architectures between x86 and openRISC but they may have other shortcomings. for example, POWER licenses were expensive as fuck and given out sparingly before IBM open-sourced it

another advantage of ARM is that ARM Holdings made decent reference designs available for use. companies can design their own chips, but they can also just take stock ARM cores and throw them in their SoCs as-is