RISC-V Vector Instructions vs ARM and x86 SIMD
Is old Cray-1 style vector machines coming back? What exactly is the difference between vector instructions and modern SIMD instructions?
In the 1980s, super-computers looked like what you see in the image below. The semi-circular shape of a Cray was synonymous with super computers in the 80s. That was just what a super computer looked like.
What does this bygone era of supercomputing have to do with RISC-V? You see, Cray computers where what we call vector processing machines. Something that has long been considered a relic of the past.
Yet RISC-V is bringing Cray style vector processing back, even insisting it should replace SIMD (Single Instruction Multiple Data). Heresy?
Such a bold and different strategy surely needs some explanation. Why are RISC-V designers taking a completely different route from their competitors x86, ARM, MIPS and others?
As usual we need a little detour to explain what exactly these technologies are and how they are different. Despite SIMD instructions coming last, I believe it is easier to grasp vector processing instructions by beginning with SIMD.
