Comment by garganzol

13 hours ago

100x speed improvement of math operations by 8087 is not an overestimation. The difference for apps relying on math was crazy back then. I experienced this first-hand on my 80286 machine, where it was 3-second vs 300-second calculation results.

One neat feature of 8087 instruction set is that it can be interspersed with x86 instructions in the code stream, giving you a simultaneous access to two processor chips working in parallel. This combo forms a real asymmetrical multi-processor system with certain opportunities for hardware-assisted code parallelization. If a thoughtful instruction scheduling is used, floating operations executed by 8087 work in parallel with the usual integer x86 code.

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garganzol

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mgaunard  10 hours ago

Any modern processor has different execution ports specialized in different things and replicated a different number of times, and all of them can execute instructions in parallel.

It schedules to these transparently for you, that's known as superscalar execution. To maximize occupation, out-of-order execution and simultaneous multithreading are used.

  • fulafel  41 minutes ago

    Transparent scheduling of superscalar execution was a later advance in microprocessors, termed out of order execution. Apart from micros both did come out around the same time in the mid-1960s.

    In the x86 microarchitectures superscalar came in Pentium and OoO got introduced in Pentium Pro.

    (Superscalar is just having >1 pipelines, which at its introduction meant needing to manually schedule your code very carefully to take advantage of it absent the OoO execution. For example the frequently posted-about Doom optimizations and talk of the u and v pipes are about this. The scheduling didn't happen transparently in early superscalars, at best the cpu automatically stalled, and some archs (eg MIPS, i860, TI C3x) even visibly punted hardware detection of pipeline hazards and required the code to just not go there, see load delay slots and branch delay slots. )