[TUHS] Why did PDPs become so popular?

Kevin Bowling kevin.bowling at kev009.com
Sat Dec 30 09:54:25 AEST 2017

I trust your judgement and experience WRT the Alpha.

If you're looking for massive performance deltas, what about ECL
designs like the IBM 3090 and Cray designs in the late '80s/ early
'90s?  I believe those were not a multiple but a magnitude faster than


On Fri, Dec 29, 2017 at 9:38 AM, Larry McVoy <lm at mcvoy.com> wrote:
> On Fri, Dec 29, 2017 at 04:04:01AM -0700, Kevin Bowling wrote:
>> Alpha generally maintained integer/ALU and clockspeed leadership for
>> most of the '90s
>> http://www.cs.columbia.edu/~sedwards/classes/2012/3827-spring/advanced-arch-2011.pdf
> Wow, that first graph is the most misleading graph on CPU performance
> I've ever seen.  Ever.
> So from 1993 to 2000 the only CPUs released were Alphas?
> That era was when I was busy measuring performance across cpus and
> operating systems and I don't ever remember any processor being a
> factor of 2 better than its peers.  And maybe I missed it, I only
> owned a couple of alpha systems, but I never saw an Alpha that was
> a game changer.  Alpha was cool but it was too little, too late to
> save DEC.
> In that time period, even more so now, you had to be 2x better to get
> a customer to switch to your platform.
>         2x cheaper
>         2x faster
>         2x more reliable
> Do one of those and people would consider switching platforms.  Less than
> that was really tough and it was always, so far as I remember, less than
> that.  SMP might be an exception but we went through that whole learning
> process of "well, we advertised symmetric but when we said that what we
> really meant was you should lock your processes down to a processor
> because caches turn out to matter".  So in theory, N processors were N
> times faster than 1 but in practice not so much.
> I was very involved in performance work and cpu architecture and I'd love
> to be able to claim that we had a 2x faster CPU than someone else but we
> didn't, not at Sun and not at SGI.
> It sort of make sense that there weren't huge gaps, everyone was more or
> less using the same sized transistors, the same dram, the same caches.
> There were variations, Intel had/has the biggest and most advanced
> foundries but IBM would push the state of the art, etc.  But I don't
> remember anyone ever coming out with a chip that was 2x faster.  I
> suspect you can find one where chip A is introduced at the end of chip
> B's lifespan and A == 2*B but wait a few month's and B gets replaced
> and A == .9*C.
> Can anyone point to a 2x faster than it's current peers chip introduction?
> Am I just not remembering one or is that not a thing?
> --lm

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