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FP/SIMD

FP/SIMD refers to a CPU's floating-point and vector registers, which hold decimal math and batched parallel data.

FP registers store floating-point numbers; SIMD (Single Instruction, Multiple Data) registers hold several values at once so one instruction can operate on all of them in parallel — the basis of fast vector math. Because each thread may leave its own values in these registers, the operating system must save and restore this state per-thread on a context switch, or one thread would clobber another's numbers.