Which Dec Emulation is the MOST useful and Versatile?

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Oct 24 13:11:49 CDT 2017

    > From: Kip Koon

    > f I were to have to decide on just one model DEC PDP system to run in a
    > DEC Emulator, which one would be the most useful, versatile and has the
    > most software available for it?

To echo what others have said, when you say 'emulator', do you mean hardware
(the usual meaning of emulator), or software (which would be a simulator)?
And if you mean hardware, are you going to emulate the bus as well?

Having said that, I think you should ask yourself 'what do you want to do
with it'? The thing is there are a lot of DEC machines which are
'interesting', and have a lot of software available for them: the -8, -10,
11, -15 and VAX (dunno if you consider that a 'PDP') are all in that category.

    > I hear a lot about the PDP-11. I found out that there were 16 major PDP
    > models at one time so I'm not too sure which one to pick.

They aren't really that different; many of them are more 'the optimal
technology to implement in' changed over the (fairly) long life of the
architecture, so many of models are where an earlier one was replaced by a
more cost-effective equivalent. E.g.  for one 'class', the /20 (TTL SSI) was
followed by the /05 (microcoded TTL SSI), and then the /04 (TTL MSI), and then
the /03 (LSI); in another the /40 was followed by the /34 and then the
/23. Etc. There are really only 3 kinds of -11:

- Those without memory management (the /20, etc)
- Those with 'simple' memory management (the /40, etc)
- Those with 'complex' memory management (all the others)

Simple software will run on all three; more complex (e.g. Unix) only on the
latter two.

    > Back in the day when Bill Gates and company 1st started out
    > ... a B/W photo of a young Bill Gates bending over the operator at what
    > looked like a very small computer. Maybe it was just a terminal. I
    > don't remember. I understand they did software development on a DEC PDP
    > of some sort. 

The very earliest version of their BASIC was done on PDP-10's running TOPS-10
- first the one at Harvard, and then some commercial time-sharing system in
the Boston area.

    > I have many projects in the works already so I decided to setup a
    > software emulation of just one of the DEC PDP models.

OK, so it's going to be just running a simulator?

    > I have heard a lot about the PDP-11 which if the information I read is
    > correct was 16-bits. in the world... The PDP-11 is the model I hear the
    > most about. 

Well, for good reason, I think.

It was at one point (1980), the best-selling computer, and really made the
minicomputer (yes, I know the -8 was the first successful mini, but their
size/computing power range was a lot smaller than the -11, and so it didn't
have as widespread a utilization as with the -11).

It's also the machine that Unix was developed on, so if you want to play
around with the 'classic' early Unixes (e.g. Version 6), you'll be wanting
to go with the -11.

Finally, it is to me the finest architecture ever, in terms of elegance, and
bang/buck - the power they squeezed into a 16-bit instruction is pretty
mind-blowing. If you want to see a really elegant design, look at the -11. A
lot of later architectures stole a lot of ideas from the -11.

If you want to go the -11/V6 route, there are instructions for doing
so here:


and I have a very detailed page for doing so with the Ersatz-11 simulator
(which is _very_ fast, and easy to work with), with a lot of useful pre-built
disks, and tools, here:


The other one I would point to as 'interesting' is the PDP-10, _especially_
if you run ITS on it. There's a very complete and detailed page here:


for bringing it up under SIMH. There's also KLH10 as a simulator, which I
know a lot of people like for running ITS; instructions here:


which has a lot of detail about how to get things running _on_ your ITS once
you have it up.

Please let us know what you decide... :-)


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