22 Apr
2024
22 Apr
'24
8:21 p.m.
Once CPUs became faster than memory the faster the memory the faster the
CPU could run.
That is where CACHE came in. Expensive small high speed ram chips would
be able to feed the CPU faster except in case of a cache miss and then
the cache had to reload from slow memory. That is why multiple cache
buffers were implemented so one could be filling (predicatively) while
another buffer was being used.
Some early CPU's were run slowly enough so that the memory could keep up
and some had built in hardware handshaking. For example the 68000 had a
signal called DTACK which was used by the memory/peripheral to say that
it had latched the data on the bus (on writes) or that the data is
stable on the bus (on reads).
Or used quadrature clocks (like the 6809 [the 6809E ran a 2 phase
non-quadrature clock]) that gave memory more than one cycle time to respond.
On 4/22/2024 3:02 PM, Wayne S via cctalk wrote:
I read somewhere that the cable lengths were expressly
engineered to provide that signals arrived to chips at nearly the same time so as to
reduce chip “wait” times and provide more speed.
So that begs a question. Older chips like the Z80 and 8080 lines required other support
chips that added latency to a system waiting for the support chips to “settle”. Does that
imply that newer microprocessors that have support on the chip are just generally faster
because of that?
Sent from my iPhone
> On Apr 22, 2024, at 12:54, Chuck Guzis via cctalk <cctalk(a)classiccmp.org>
wrote:
>
> On 4/22/24 12:31, ben via cctalk wrote:
>> Classic cpu designs like the PDP-1, might be better called RISC.
>> Back then you matched the cpu word length to data you were using.
>> 40 bits made a lot of sense for real computing, even if you
>> had no RAM memory at the time, just drum.
> I'd call the CDC 6600 a classic RISC design, at least as far as the CPU
> went. Classes were given to programming staff on timing code precisely;
> I spent many happy hours trying to squeeze the last few cycles out of a
> loop (where the biggest bang for the buck was possible).
>
> I think bitsavers (I haven't looked) has a document or two on how to
> time code for that thing.
>
> --Chuck
>
>