Between the ARM and MIPS processor ISAs, why did smartphone makers go with ARM?

Question

I know the first iPhone used an ARM CPU. I don’t know what CPU ISAs were common in smartphones before the iPhone.

In: Technology

Answer 1

Choosing ARM over MIPS was most likely a business decision instead of a technological one.

There are two fundamental kids of ISA: RISC and CISC

* In a RISC (Reduced Instruction Set Computer) ISA, each individual instruction does one specific thing, such as a load from or store to memory, a mathematical operation or a branch. RISC ISA are generally easier to design and they can provide more hardware optimizations than CISC. Both ARM & MIPS are RISC architectures.

* CISC (Complex Instruction Set Computer) were invented first and each instruction can do several things at once. A single CISC instruction could fetch a value in memory, and use that value that as the address to write a register value to memory as well as branch at the same time. These meant on early machines that had every limited memory space, you could potentially fit in more instructions. x86 was originally designs as a CISC architecture, but modern implementations are RISCs with as micro-programming layer between the physical hardware and the machine code, allowing many legacy programs to be run on newer hardware.

There are actually many more kinds of ISA, and GPUs are based around a radical different design paradigm, but for CPUs, it’s pretty much RISCs and CISCs and RISCs have basically won.