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From: Jon Steinhart <jon@fourwinds.com>
To: TUHS main list <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] Encoding an ISA: Random Logic vs. Control Stores
Date: Tue, 30 Nov 2021 21:00:36 -0800	[thread overview]
Message-ID: <202112010500.1B150a48077541@darkstar.fourwinds.com> (raw)
In-Reply-To: <CAEdTPBeiXo1fU+JSnnR1OT=0YuXCCsUU9tPsrOLbGKqE8zeZ_w@mail.gmail.com>

Henry Bent writes:
> On Tue, 30 Nov 2021 at 18:10, Jon Steinhart <jon@fourwinds.com> wrote:
>
> > Humm writes:
> > > Quoth Jon Steinhart:
> > > >arnold@skeeve.com writes:
> > > >> Can someone please explain why it's called "random" logic? Discrete
> > > >> logic I understand (more or less), but I've not heard the term
> > "random"
> > > >> used in this context before now.
> > > >
> > > >Well, as a recovered random logic designer, I think that the name comes
> > > >from there being no particular structure to the logic.  Many parts of
> > > >logic design are very regular, think memory.  But that regularity doesn't
> > > >exist when, for example, decoding irregular instructions.
> > >
> > > Now that's a "random" definition.
> > >
> > > --
> > > Humm
> >
> > OK, I'll try again.  For anybody familiar with Portland, Oregon, it's the
> > difference between driving in Northwest where there's a rectangular grid
> > numbered in one direction and alphabetical in the other, and approaching
> > the Ross Island Bridge from the west side which appears to be designed by
> > someone following a goat while tripping their brains out.  One can address
> > Northwest Portland quite easily unlike getting onto the Ross Island Bridge.
> >
>
> So - and as I say this as someone who has no direct experience with this
> level of logic - everything is directly addressable but the difference is
> in how you get there?

Sorry my analogy didn't work.  Look at a photomicrograph of a chip; at least
to me it's pretty obvious where the random logic is located.

Here's another try.  In a microcoded machine, the same hardware is used for
every microinstruction.  In random logic, custom designed circuitry is used
for each special case.

  reply	other threads:[~2021-12-01  5:02 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-30  8:07 pbirkel
2021-11-30 15:19 ` Ron Natalie
2021-11-30 15:30   ` arnold
2021-11-30 15:39     ` Ralph Corderoy
2021-11-30 18:50     ` Jon Steinhart
2021-11-30 21:45       ` Humm
2021-11-30 23:07         ` Jon Steinhart
2021-11-30 23:18           ` Henry Bent
2021-12-01  5:00             ` Jon Steinhart [this message]
2021-12-01  6:27               ` pbirkel
2021-12-01 16:42                 ` ron minnich
2021-12-01 17:08                   ` Ron Natalie
2021-12-01 21:56                   ` [TUHS] Encoding an ISA Warren Toomey
2021-12-01 13:59 [TUHS] Encoding an ISA: Random Logic vs. Control Stores Paul Ruizendaal
2021-12-01 14:55 Douglas McIlroy
2021-12-01 20:27 ` Jon Steinhart
2021-12-01 21:14 ` Lawrence Stewart
2021-12-01 22:09   ` Jon Steinhart

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