From: alderson@elaine46.Stanford.EDU (Rich Alderson)
Subject: Re: PDP ftp archive
Originator: alderson@leland.Stanford.EDU
Reply-To: alderson@elaine46.Stanford.EDU (Rich Alderson)
Organization: Stanford University Academic Information Resources
Date: Mon, 23 Nov 92 18:56:07 GMT

In article <1992Nov22.114337.15485@news.columbia.edu>, lasner@watsun (Charles Lasner) writes:
>In article <1992Nov21.003656.17491@leland.Stanford.EDU> alderson@elaine46.Stanford.EDU (Rich Alderson) writes:
>
>>>	PDP-6                  36    DEC's first really big computer.
>>
>>				     (only 23 were ever built, cause KO hated
>>				     big MIS-type machines)
>
>I heard it was 20, not 23.

The number 23 was mentioned in the K. Olsen bio _The Ultimate Entrepreneur_.  I
think I also heard it from a friend who managed 36-bit engineering at DEC.

>
>>>	PDP-10 1967            36    A PDP-6 upgrade, great timesharing.
>>
>>				     Not exactly--more a revival.
>
>Upgrade is an unfortunate word.  I think the reference is to the fact that
>they are instruction-set compatible, and that time-sharing didn't really
>happen on a -6.

Note the number of attribution arrows.  *I* was objecting to calling it an
upgrade.  The *PDP-8 FAQ* calls it an upgrade.

>>	Hmmph.  Leave it to the 12-bit crowd to get it wrong.
>
>Not as far wrong as these guys posting about "PDP's" as if -11's are the
>only kind!

Amen!

>>
>>	The DEC-20 is the outgrowth of a smart decision by DEC:  License the
>>	TENEX operating system written for the Dec-10 by Bolt, Beranek, and
>>	Newman, which featured real demand-paged virtual memory, and sell it
>>	as an *alternative to*, not a replacement for, Tops-10, which was the
>>	descendant of the *batch-processing* operating system on the PDP-6 and
>>	early PDP-10s.
>
>But the -20 *is* a -10.  What's the difference between a KL-10 and the
>high-end -20, the color of the cabinet?  Yes, you don't run TOPS-20 on
>a KA-10, but a KL can be called anything you want.  The point is that model
>numbers can be muddled, and clearly marketroids are the source of the
>muddling.  Calling them all -10's would've been fine, but...

There are microcode differences between a DEC-20 and a Dec-10--the JSYS
instruction, for example, as opposed to UUOs.  The question is not what the
*hardware* is--yes, a KL is a PDP-10 and can be either a DEC-20 or a Dec-10--
but rather what the *12-bit* crowd knows about the differences.

And you can't run TOPS-20 on either a KA or a KI, only on a KL.

>Also, what about the ill-fated Jupiter?  Wasn't that to be "doubled" again
>and be renamed DECsystem-40?

This requires a bit of digression on the model-numbering scheme.  I don't know
all the numbers for the Decsystem-10, but a couple of important ones are the
1050 (which gave its name to the Tops-10 compatibility package on TOPS-20), and
the 1090 and 1091 (which were the high-end systems, differing in that the 1090
used core and the 1091 used MOS memory--or so *I* was told by an FE friend.)

(Yes, I was friends with my FE.  Wanna make something of it? :-)

The original DEC-20...

(BTW, I tend to use the capitalizations common to manuals from Digital.  Thus,
the older system was the Decsystem-10 or DECsystem-10 and ran Tops-10, while
the later system was the DECSYSTEM-20 and ran TOPS-20.  Back to our story...)

The original DEC-20 was the KL-10 model 2040.

The next model was the 2050, which used a cache memory to speed up the demand-
paged virtual memory.

The final model was the 2060, which came in two flavours, depending on whether
the box implemented "extended addressing"--that is, the original 18-bit address
space was expanded to 30 bits in the Model B, while the Model A did not have
this capability.  The Model A would run versions of Tops-20 up to version 4;
later versions would only run on the Model B.

I said "final model" in the previous paragraph, but there are two things to
add.  The 2020 was a small machine, which was sort of a work-group version of
the architecture.  It did not have extended addressing, and ahd slightly
different I/O instructions from the other -20's.

The 2065 was an upgrade of the 2060--both models--with a larger, faster cache.

Now, given all this, the original model number for the Jupiter was 2090.
However, I was given a Sales Training Seminar binder for the never-introduced
Jupiter which is labeled DECsystem-4050.
-- 
Rich Alderson   'I wish life was not so short,' he thought.  'Languages take
                such a time, and so do all the things one wants to know about.'
                                                        --J. R. R. Tolkien,
alderson@leland.stanford.edu                              _The Lost Road_
Newsgroups: alt.folklore.computers