[TUHS] Why did PDPs become so popular?

Kevin Bowling kevin.bowling at kev009.com
Fri Dec 29 21:04:01 AEST 2017

I can mostly only comment from my readings, but this is IMHO a
non-trivial question even in retrospect because it depends on what you
or your workload valued.  I do like how lmbench categorizes across
multiple "interesting" vectors, showing some of the design tradeoffs
of CPU architecture and then how the OS plays a role in real world

Alpha generally maintained integer/ALU and clockspeed leadership for
most of the '90s

For intel the Pentium Pro was pivotal in being able to position vs the
contemporary RISC CPUs with multi-MB caches.  And federating cost
effective CPUs together with Laissez-faire mainboard/system
packaging/OSes turned out to be more important than pretty much
anything else.

I know that IBM Austin did some wizard of oz stuff in early POWER..
Bi-CMOS superscalar that put it 4-5 years ahead of most competing
microprocessor designs in floating point, though SGI and HP traded
respectable volleys.  But POWER also had fat memory bandwidth, they
tended to make well balanced braniacs that didn't blindly pursue the
clockspeed war (http://www.cs.virginia.edu/~mccalpin/papers/balance/).
They got into a weird spot in the second half of the 90s with an
out-dated bus, internal competition from PowerPC and RS64, but
returned to leadership with POWER4 and up to today. POWER's IO
leadership made it a good fit for many early internet routers in the
early '90s, NSFNET and others.  Interestingly modern POWER retains
that leadership on memory and I/O which can put it 2 to 4 years ahead
of everything else depending on what you value (Google seems to see
the light using it for gluing GPUs together..).  From IBM Rochester,
RS64 was kind of interesting in being the first use of SMT and having
incredibly low TDP which were both interesting clairvoyance into the
next decade.

In retrospect I don't think SPARC ever had a reasonable showing pound
for pound vs other microprocessors :)


On Thu, Dec 28, 2017 at 4:28 PM, Theodore Ts'o <tytso at mit.edu> wrote:
> On Thu, Dec 28, 2017 at 08:08:11AM -0800, Larry McVoy wrote:
>> > I think you're right.  The disinterest in marketing and advertising
>> > (Ken Olsen, and therefore DEC, had a "build it and they will come"
>> > mentality) was one aspect of the corporate culture.  An example of its
>> > negative impact:  When the Alpha EV5 came out, it was several times
>> > faster than anything else around.
>> Got a reference for that performance claim?  Wasn't that mid 1990's?
>> If so, I was heavily into benchmarking and performance work during
>> that period.  If there was a processor that was 2x faster, let alone
>> several times faster, I would have noticed.
>> http://www.bitmover.com/lmbench/lmbench-usenix.pdf
> "Digital's 21164 Reaches 500 MHz: Alpha Regains Performance Lead,
> Leaves Pentium Pro in Dust" -- Microprocessor Report July 8, 1996.
> http://noel.feld.cvut.cz/vyu/scs/alpha/164_500.pdf
> Looks to me from the article that Alpha was certain participating in
> the clock speed wars, though.
>                                         - Ted

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