PDP Lineage

From [email protected] Thu Jan 25 19:15:51 1990
Newsgroups: alt.folklore.computers
Subject: DEC's PDP family tree
From: [email protected] (Bob Devine)
Date: 22 Jan 90 23:05:44 GMT
Organization: Digital Equipment Corp. - Colorado Springs, CO.

In the beginning was the PDP-1 ...
PDP-1 = first commercial interactive computer; late 1960; had 18 bits
PDP-2 = a PDP-1 with another mem board
PDP-3 = A DEC customer (Scientific Engineering Institute, Waltham, Massachusetts) built a PDP-3 in 1960. It finally was given to M.I.T., and eventually wound up in Oregon (1974).
PDP-4 = a modified PDP-1
PDP-5 = "first minicomputer" introduced in early 1963
PDP-6 = a 36-bit machine; came out in late 1964
PDP-7 = a modified PDP-4
PDP-8 = successfully mass-produced follow-on to PDP-5; 1965
PDP-9 = a modified version of the PDP-7 (it started life as a PDP-7/X). Its main advance over the PDP-7 was in the memory design.
PDP-10 = follow-on to PDP-6; 1967
PDP-11 = an entire family of these 16-bitters was made; 1970
PDP-12 = sort of a PDP-8 merged with the LINC machine
PDP-13 = no such machine!
PDP-14 = some sort of industrial computer
PDP-15 = a whole family of computers (the PDP-15/10, /20, /30, /35, /40, /50, and /76). One of the first DEC computers to use ICs extensively. First PDP-15 shipped in February 1970.
PDP-16 = some sort of industrial computer

The family tree goes something like this:
PDP-1 --> PDP-4 --> PDP-7 --> PDP-9 --> PDP-15
PDP-5 --> PDP-8 --> PDP-12
PDP-6 --> PDP-10 --> DECsystem-10 --> DECsystem-20
PDP-11 --> VAX

A good overview of the DEC family of computers can be found in the book "Computer Engineering - A DEC view of hardware systems design", by C. Gordon Bell, J. Craig Mudge, and John E. McNamara. It is published by Digital Press, ISBN 0-932376-00-2.

From [email protected] Thu Jan 25 19:15:20 1990
Newsgroups: alt.folklore.computers
Subject: PDP-9T in DEC's heritage
From: [email protected] (Martin Taylor)
Date: 23 Jan 90 00:18:51 GMT
Reply-To: [email protected] (Martin Taylor)
Organization: D.C.I.E.M., Toronto, Canada
Summary: DEC's first memory mapped time-sharing machine

Brian Stuart gave a nice chart of the DEC family of computers:

Year  18-bitters     12-bitters         16-bitters                 36-bitters
1960    PDP-1 -------------------------------------------------------
          |                                                          \
1962    PDP-4 <--- LINC --------                                      \
1963      |        PDP-5   \    \                                      |
1964    PDP-7        |      \    \                                   PDP-6
1965      |        PDP-8 --\ |    \                                    |
1966      |        PDP-8/S LINC-8  |                                   |
1967      |          |       |     |                                 KA10
1968    PDP-9      PDP-8/I,L |     |                                   |
1969      |          |     PDP-12  |                                   |
1970    PDP-15       |           PDP-14  PDP-11(/20)                   |
1971      |        PDP-8/E                /   |  \                     |
1972    PDP-15/76  PDP-8/M        - PDP-11/05 | PDP-11/45 --         KI10
1973                 |           /   |    PDP-11/40  |      \          |
                     |          /    |         |     |       \         |
1975               PDP-8/A PDP-11/03 PDP-11/04 |     |    PDP-11/70  KL10
1976                 |            PDP-11/34    | PDP-11/55    |      KL20
1977               VT78              |    PDP-11/60           |
1978                              PDP-11/34C              VAX-11/780

but at least one is missing: the PDP-9T of 1967-8. This was, as far as I know, DEC's first memory mapping computer designed for real-time time-shared experiment control. (I know the PDP-1 was time-shared, after a fashion, but the 9T had proper separation of all address spaces, round-robin scheduling, and so forth).

The story is more or less as follows: DCIEM had been looking for a shared experiment controller, and I was considering whether we could modify a PDP-7 along the lines of the SDS-940 at Berkeley(? where Butler lampson was, if not Berkeley). DEC's Canadian salesman, Sy Lyle, took my proposal to Maynard, and came back with stories of this wonderful new super-PDP-7 on which we might try the idea if we could persuade the project manager, John Jones. So off I went to Maynard, on the way passing by Harvard Psych Department, where they were in the planning stage of buying 4 IBM 1800s for experiment control. There I got Dan Forsythe and Don Norman interested, and we all went to see John Jones in the old mill in Maynard. After a few minutes of my presentation, he asked us to wait while he called in his Chief Engineer, Larry Seligman, who listened for about 20 minutes. Jones asked him what he thought, and he said "I like it," so Jones said "We'll do it."

That's the kind of company I like.

So what happened? Harvard and DCIEM both bought one, but San Diego did not, and neither did anyone else. The Harvard and DCIEM machines were developed in parallel with the normal PDP-9, leapfrogging each other in the development of their time-sharing hardware. Seligman devised a neat instruction-mapping device that allowed individual users to have their own privileged instruction sets and enabled them to exercise direct control over their I/O devices (wild, for a fully protected real-time time-sharing machine; I often wonder why it was not ported to the PDP-11 along with the memory mapping scheme).

Unfortunately, in the middle of the PDP-9 development, Seligman went back to university, leaving the PDP-9 in the hands of a less imaginative Chief Engineer. The PDP-9 that Seligman designed was later built, and called the PDP-15 (at least many of the characteristics of the PDP-15 were those Seligman had specified for the PDP-9 but did not appear in the 9). As a result, the actual PDP-9T was not the clean machine that it should have been. DEC never produced any software for the 9T, and as far as I can gather, never tried to sell any other than the two development machines. But those two ran experimental psychology labs for over a decade, quite successfully.

The PDP-9 had an address space of 32K 18-bit words, but the mapped machine allowed 256K. The virtual machine seen by the users was identical to a normal PDP-9 except for the 256 extra instructions provided by Seligman's I/O mapping trick, some of which did virtual DMA for non-DMA devices, provided timing services, and the like (for real-time experiments). On the normal PDP-9, the user had to use a minimum of 8K because of the ADSS monitor, but on the 9T, the user could be as small as 2K, which was plenty for many experiments. Users were guaranteed a response to an interrupt within 10 msec, and usually got it within 2 msec (all in-core, there was no swapping), with as many as 10 real-time users. Scheduling was a round-robin with 1 msec frames.

The PDP-9T inspired two sharp characters from Harvard, Rob Strom and Bob Walton, to produce both software and theoretical studies of time sharing. Walton, in particular, devised a theory of guaranteed real-time time-sharing that was not put into practice (as far as I know) until perhaps 10 years later on the PDP-11/34 and 11/70, with our (DCIEM and Andyne Computing Ltd.) MASCOT modifications to the UNIX kernel. The software development for the machine was a joint project of Harvard Psych Department and DCIEM.

Fun Days, with a Fun Machine. I wish DEC were like that now!

Martin Taylor ([email protected] ...!uunet!dciem!mmt) (416) 635-2048
If the universe transcends formal methods, it might be interesting.
(Steven Ryan).

From "The PDP-11 FAQ" ftp://ftp.update.uu.se/pub/pdp11/faq

=====  ====  ========  ====  =====
PDP-1  1960  $120,000  18    DEC's first computer
PDP-2            NA    24    Never built?
PDP-3                  36    One was built by a customer, none by DEC.
PDP-4  1962            18    Predecessor of the PDP-7.
PDP-5  1963   $27,000  12    The ancestor of the PDP-8.
PDP-6  1964  $120,000  36    A big computer; 23 built, most for MIT.
PDP-7  1965  ~$60,000  18    Widely used for real-time control.
PDP-8  1965   $18,500  12    The smallest and least expensive PDP.
PDP-9  1966   $35,000  18    An upgrade of the PDP-7.
PDP-10 1967  $186,500  36    A PDP-6 successor, great for timesharing.
PDP-11 1970   $10,800  16    DEC's first and only 16 bit computer.
PDP-12 1969   $27,900  12    A PDP-8 relative.
PDP-13           NA          Bad luck, there was no such machine.
PDP-14                       A ROM-based programmable controller.
PDP-15 1970   $16,500  18    A TTL upgrade of the PDP-9.
PDP-16 1972 $.8-$4,000 NA    8/16  A register-transfer module system.

Since then, the PDP-11 had 16 to 22 implementations, depending on how you count them, many with variants. The following attempts to briefly track the evolution and progression.

In 1969 the -11 family was projected as follows:

Model  CPU   Comments

11/20 KA11 Origin of the species 1x performance. 11/10 - .7 of the 11/20, technologically cost reduced 11/20 in MOS. [This obviously became the 11/05, 11/10] 11/30 KA11 [Seems to have been the same as an 11/20 packaged with a little more memory, etc. I believe this is what eventually became the 11/20 that actually shipped] 11/40 KB11 2x performance. 11/45 KB11 2x performance. [Seems to have been intended to be an 11/40 with MMU. [Looks like this became the 11/40 that eventually shipped.] 11/50 KC11 2x performance. Hardware floating point 32 bit processor. [I believe the 32 bit refers to the FPU!] 11/55 KC11 2x performance. With MMU. [It looks like the 11/50 plus 11/55 became the eventual 11/45] 11/65 KD11 4x performance. 32 bit separate memory bus, 32 bit processor.

PDP-11 Operating Systems

    Resource Sharing/Time Sharing. General purpose Time sharing system.
    Cassette Based Programme development System.
    Massachusetts General Hospital Multi-User Multi-Processing
    System.  A language, an operating system and a DBMS all in one.
    Real Time. Foreground/Background or Single Job operating system. 
    Multiuser enhancements to RT11 (third-party).
    Resource Sharing eXecutive. Multiprogramming system.
    Small to moderate-sized real-time multiprogramming system.
    Extended RSX-11/M.
    Execute-only real-time multiprogramming system.
    Large real-time multiprogramming system.
RSX-11B/C, Micro/RSX
    Interactive Application System. Multi-purpose multiprogramming system.
    Transaction Processing system.
Unix (tm)
    Much/most of Unix was developed on PDP-11s.
    A virtual operating system that could run Unix as
    a process.  Several machines at BTL ran MERTS.
    There's some confusion as to whether this is just a re-packaged
    version of RT-11, or a time-sharing system layered on top of RT-11.
    There's some confusion as to whether this is just a re-packaged
    version of RSTS, or a time-sharing system layered on top of RSTS.
    Time-sharing system layered on top of RT-11.
    Heathkit's hacked version of RT-11, wouldn't run on a "real" PDP-11.
    Digital's implementation/port of BSD UNIX.
    A third-party implementation/port of UNIX.

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