14 Jun
2024
14 Jun
'24
8:13 a.m.
On Jun 13, 2024, at 7:31 PM, ben via cctalk
<cctalk(a)classiccmp.org> wrote:
On 2024-06-13 11:32 a.m., Paul Koning via cctalk wrote:
e up an entire chassis, 750-ish logic modules.
But I want to know, how to compare machines if you can't compare the logic.
You compare machines by what they deliver. The purpose of computers is not to deliver
logic circuits but to deliver computation, so comparing computational ability (speed and
size) is meaningful, along with cost. How it's implemented under the covers is not.
Yes, the implementation details affect the user's figures of merit, but those figures
and not the logic choices made by the designers matter.
paul
You never see a gate level delays on a spec
sheet.
Our pipeline is X delays + N delays for a latch.
Gate level delays are not
interesting for the machine user to know. What is interesting is the detailed properties
of the pipelines, including whether they can accept a new operation every cycle or just
every N cycles (say, a multiplier that accepts operands every 2 cycles); how many cycles
is the delay from input to output; and whether there are "bypass" data paths to
reduce the delays from input or output conflicts. Often these details are hard to pry out
of the manufacturer; often they are not documented in the standard data sheets or
processor user manuals. But they are critical if you want to do work such as pipeline
models to drive compiler optimizers.