>glen herrmannsfeldt wrote:

> >dave@mynatt.biz wrote:

>> I'm the program director for a non-profit in Colorado and I am looking
>> for a PDP-11 that we could use to train students with and to introduce
>> them to our beginnings. I know PCs are available for emulation and
>> used instead, but I was hoping someone may have a surplus, give away
>> PDP-11 or other mini-mainframe that we could pick up and cart away.

> There may be enough LSI-11 machines around that you might find
> one for a low price.

Jerome Fine replies:

In addition, if it is really important to run on an actual DEC PDP-11 CPU,
you may find that it takes more than one acquisition to acquire a complete
working system. Very often, after you find one portion of a system, other
parts will become available soon after.

As for using an emulator, I find that they run the software just as well as
the real PDP-11 hardware, but without all the difficulty of finding a
complete working system. So why not use a combination of both
types of hardware. One real DEC PDP-11 CPU along with an old
serial terminal such as a VT100 or a VT220 is probably sufficient to
demonstrate how a real DEC PDP-11 looks and feels, but I suggest
that only a few dedicated PDP-11 hardware addicts would insist on
a real DEC PDP-11 CPU all the time.

In that regard, SIMH is licensed to run up to V05.03 of RT-11 which
is available for download at:
The file RT11DV10.ISO.zip holds most of the RT-11 binary distributions
from V1-15 up to V05.03 of RT-11. bitsavers also has RT-11 manuals
available in PDF format.

Hopefully, hobby users will soon be able to use E11 as well to legally
run RT-11 and maybe somehow V05.07 of RT-11 will become legally
available to hobby users to run as well, although this situation has been
ongoing for MANY years and does not seem likely (i.e. with versions
of RT-11 after V05.03) to be resolved for another decade or two.

I find that the primary advantage of E11 (since I have a number of
legal RT-11 licenses that I can use) to be the built-in VT100 emulation
as well as the extra speed. E11 runs more than 100 times faster vs a
real DEC PDP-11/93 on a high end Pentium Quad CPU and the disk
I/O with SATA II hard drives is even faster.

So by all means have one demonstration DEC PDP-11 CPU. But if
you are attempting to demonstrate the software, I really can't see the
advantage of insisting on original hardware.

>> I'm not sure such a thing exists, but if I don't ask I'll never know
>> and it would be a great addition to our program if we could get one. I
>> used a PDP-11/45 when I worked for AT&T and thing if I could load an
>> OS and a compiler of some type it would be a great learning tool.
>> Almost anything with lights, tape deck, big disks and such would fill
>> the bill.

> Disks and tapes are more of a problem. With moving parts they
> tend to be less reliable. Floppies yes, but anything else will
> cause lots of problems if you do manage to find one.
> 8 inch drives aren't so hard to find, but HD 5.25 or 3.5in
> drives can be interfaced to an 8 inch controller, and will
> be much easier to find media for.

A word of caution. The 5 1/4" RD53 (Micropolis 1335) heads tend
to stick. Other hard drives are longer lasting. Personally, I use
Hatachi 5 1/4" ESDI drives on the real DEC PDP-11/83 CPU
in a BA123 box.

> 9-track tape drives will be expensive and lots of work.

The TK50 is too slow to be really useful. The TK70 is much
more reliable as well. Both use the same CompacTape I or II
media, although you MUST blank erase to switch from the
TK50 to the TK70. Both of these tape drives are 5 1/4"
and fit nicely into a BA23 or BA123 box. But they are not
very flashy and probably don't look much different from any
DLT tape drive.

> SCSI for Q-bus tends to be expensive, but would work with
> easily available drives. It shouldn't be hard to interface
> IDE/ATA to Q-bus, and not so hard to write the driver, either.

The drives tend to be VERY inexpensive (50 pin header with
separate power cable) at 4 GB or less. But a Qbus host
adapter (CMD CQD220TM) is still expensive.

> Anything other than an LSI-11 is probably too collectable
> to be given away

Not always true. I can't seem to find anyone who will pick
up any PDP-11 hardware in Toronto. I have enough BA23
boxes and boards to put together a number of working systems
Maybe next year I will drive to Ohio and sell a few of them.

> There are people interfacing front panels with lights and
> switches to emulators to allow the look and feel without
> the old hardware to keep maintaining.
> -- glen

Probably useful for the really addicted hardware types, but
a PDP-11/73 in a BA23 box has no lights or switches to
speak of and looks close enough to a PC (waiting for the
claims to the contrary) that a windows Dummy might not
even notice. The PC I use to run E11 is much taller than a
BA23 (24 1/2" high) and has TEN 5 1/4" full height bays
(well half height for an RD53 drive bay). I use three 160 GB
hard drives to hold all the files I want online. There is a SCSI
Adaptac 2940AU host adapter that I can use to run SCSI
hard drives from the real DEC PDP-11/83 just as they ran
on that system along with an Iomega SCSI insider or a Sony
SMO S-501 on the odd occasion when I want to transfer
files between to real DEC PDP-11/83 and what I run under

In summary, one real DEC PDP-11 CPU is nice to be able to
demonstrate the real DEC hardware for those who care. For
the software addicts (like myself - and there are probably no
others on this list), it does not seem to matter if I run under SIMH
or E11. The PDP-11 operating system (RT-11 in my case) is
what is important. I bit of a tired refrain - my goal is to enhance
RT-11 to allow dates up to the year 9999 CE or what I call Y9K
compliant along with other enhancements such as an LA: (Logical
Assigned Lookup List pseudo device driver) which acts like the
LNL (Logical Name List under VMS) or the PATH Name in DOS.

Sincerely yours,

Jerome Fine