On Mon, Jun 10, 2024 at 05:18:56PM +0100, Joshua Rice via cctalk wrote: [...] > DEC came across another issue with the PDP-11 vs the VAX. Although the > pipelined architecture of the VAX was much faster than the PDP-11, the > actual time for a single instruction cycle was much increased, which led > to customers requiring real-time operation to stick with the PDP-11, as it > was much quicker in those operations. This, along with it's large software > back-catalog and established platform led to the PDP-11 outliving it's > successor.
Fun factoid: despite modern x86 being clocked ~1000x faster than ye olde 6502, there's not much in it between them when it comes to interrupt response time. If all goes well, x86 takes "only" a hundred-ish cycles to do its book-keeping and jump to the ISR, but if SMM is active (spoiler: it always is and you can't turn it off) then it introduces a massive amount of extra jitter and all bets are off.
