12 Jun
2024
12 Jun
'24
4:02 a.m.
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.