[TUHS] Why did PDPs become so popular?

Clem Cole clemc at ccc.com
Thu Dec 28 07:51:54 AEST 2017


You are mixing a couple of different stories I fear...

If you want the full story get a copy of:   Computer Engineering: A DEC
View of Hardware Systems Design
<https://www.amazon.com/Computer-Engineering-Hardware-Systems-Design/dp/1483207676>

But a snap shot for this mailing list is this ...  The PDP term was used by
KO when he was funding Digital because the VC's the 60s did not believe
that a computer company would succeed.   But making things for the
instrumentation market (Lincoln Labs, Livermore, *etc*.).   This is how
PDP-1 came to be.  The PDP term was keep for the first 25 years (until the
Vax and renaming of the PDP-10/PDP-20 to DECSystem 10/20). [The 1 begat the
6, 9, 15 an 10 families].

The concept of purchasing smaller system, was indeed true.   This was the
idea behind the >>mini-computer<< or *minimal computer* that Gordon Bell
who lad left DEC temporarily to be a CMU Prof for a time began to explore.
 He took the idea and commercialized and the PDP-8 line was the first in
that line.  The 11 & 15 were full computer systems.  DEC also made
something called the PDP-16 'Register Transfer Modules' (RTMs) which was an
attempt to make the small controller idea even more accessible, but the
Intel microprocessor would eclipse them (I think I was the last group at
CMU was talk a course using them.   Another factoid, the predecessor to
VHDL/Verilog and the like, ISPL and ISPS actually spit out 'code' for DEC
RTM modules instead of gates).

But the key point is that in 1975 dollars, a PDP-11/40 system that was good
enough to run something like Sixth Edition of UNIX cost somewhere between
$50k-$150k.   This would have been much, much cheaper than say a PDP-10, or
a equivilent IBM 'mainframe' size system which would have started above $1M.

Clem

On Wed, Dec 27, 2017 at 4:02 PM, Alec Muffett <alec.muffett at gmail.com>
wrote:

> I apologise if this is too far from the main topic, but I wanted to check
> an urban legend.
>
> There is a story - as I have heard it told - that PDPs established their
> place (and popularity) in the marketplace by pointedly *not* advertising
> themselves as "computers", but instead as "programmed data processors".
>
> This was because - so the story goes - that everyone in corporations of
> the time simply *knew* that "computers" came only from IBM, lived in big
> datacentres, had million-dollar price-tags, and required extensive project
> management to purchase; whereas nobody cared enough about a thing called a
> "programmed data processor" to bother bikeshedding the
> few-tens-or-hundreds-of-thousands-of-dollars purchase proposal to an
> inevitable death. Thus, they flitted under the purchasing radar, and sold
> like hotcakes.
>
> I wonder: does this story have substance, please?
>
> Aside from anything else: I draw parallels to the adoption of Linux by
> Wall St, and the subsequent adoption of virtualisation / AWS by business -
> now reflected in companies explaining to ISO27001 auditors that "well, we
> don't actually possess any physical servers..."
>
>     - alec
>
> --
> http://dropsafe.crypticide.com/aboutalecm
>
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