PDP-11/20 vd one that just says pdp 11 what are the date differences?? OEM?

Paul Birkel pbirkel at gmail.com
Mon Feb 22 07:01:15 CST 2016

IMO a lot hinges on understanding the differences between the KA11 and KH11-A processors.  As was sometimes the case, DEC "marketing" models can hide differences under the hood over time.


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of 
> Christian Corti
> Sent: Monday, February 22, 2016 4:32 AM
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: RE: PDP-11/20 vd one that just says pdp 11 what are the date differences?? OEM?
> On Mon, 22 Feb 2016, Paul Birkel wrote:
> > My PDP-11 is labeled as "S-386" and dated 9/23/70, which I guess 
> > makes it fairly early in the production run (but I do wonder what 
> > the initial manufacturing rate was given the relative riskiness of 
> > this new architecture).  Anyone have S# and dates for "plain 11" vs.
> > 11/20-marked for comparison?
> Our PDP-11 is labeled as "S-308", the date is 9/16/70. And I think 
> they called it PDP11-20 from the beginning, as the model number above 
> the serial number says "M11-20"
> Christian

I have an original 1969 PDP 11 brochure.  In it there are two PDP 11 model configurations to choose from; the 10 and the 20.  For me at least this throws into question the whole "...the 10 first came out with the 5 in1972..." story everyone repeats over and over, unless one must have a "10" printed on the console in order to accept a computer model's existence.  DEC must not have sold many original 10 models, and/or everyone who has a 10 does not realize that's what they have.  But, facts are facts and the brochure and price guide I have is what it is.  Hoping some here will check for themselves and consider it misleading at least to simply call the original PDP-11 a "pdp 11/20 without the nameplate".  In short, the original bare-bones pdp11 was the pdp-11 10, the fully-equipped version was the pdp-11 20.

Why DEC temporarily dropped it's pdp-11 10 model from the product line and from newer price sheets I can't say.   Certainly the "10" was gone when DEC rebranded their front nameplates to read "pdp 11/20".  I believe the 1969 brochure is on bitsavers, or I think my website has a copy you can download.

Bill Degnan
twitter: billdeg

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