building a PDP11 from the things you find at home

From: Jerome Fine <jhfine_at_idirect.com>
Date: Sun Jul 29 18:04:33 2001

>R. D. Davis wrote:

> >On Thu, 26 Jul 2001, Jerome Fine wrote:
> > While I probably don't really understand someone who's goal is using the
> > original hardware, on the other hand, I find that any software development
> Hmmmm, this IS the classiccmp list isn't it?

Jerome Fine replies:

Thanks for your comment - I had a good laugh. Also with a bit of tongue in
cheek, a reply ...

Yep! It includes those nerds who need to hear the screech of a disk drive
bearing gone bad (the RD53 whine is about the best) and the broken back
achieved while lifting an RA81.

It also includes those software nuts like myself who will work for a few months
to reduce the size of a program that almost no one uses anymore or output
an error message than can be understood to a user who does not exist.

I will admit that on occasion, I do delight in using VERY OLD hardware.
About 2 years ago, I needed to transfer some data to a real DECTape II
on a real TU-58 tape drive. However, the FINAL goal was to connect
the TU-58 external tape drive to a PC running the emulator for the PDP-11.
I don't know if anyone still uses a real DEC TU-58, but it is still just as slow
on a PDP-11/93 as it was on an LSI-11/2, so of course, it is no faster
on a Pentium 166 MMX. In any case, I finally got the external TU-58
connected again first the the real PDP-11 and then to the PC on a COM2:
port and copied the files. Then I was able to find a very old version of
V 3.0B of RT-11 that was on a TU-58 tape that still worked. WOW!!
After 2 minutes it actually booted RT-11. Worked just fine.

Then, just to put the icing on the cake, I copied the files from a V5.04G
of RT-11 (that I had enhanced to be Y2K compliant) to the TU-58
and was again able to boot RT-11 (after the customary 2 minutes).

Now that was a thrill - running a 25 year old tape drive first with
a 25 year old version of the RT-11 operating system on a Pentium 166 MMX
(using the emulator of course), and second with a10 year old version of
the RT-11 operating system which had been Y2K enhanced so that I could
use dates after 1999.

Actually, I think both the hardware and software goals that we have are
crazy, but since we all seem to enjoy ourselves and I know of no law
that is being broken that will need to be invoked to slowly lower us feet
first into molten iron, it seems harmless enough.

> > under an emulator is much more straight forward, much easier AND MUCH
> > FASTER.
> ...and emulators are very, very, boring; and, if run under M$-Windoze,
> much less reliable and more likely to crash or lose data. The sound
> of fans, the chatter and kerchunking of disk drives, the clicking
> contactors when mains power is applied, the vacuum and whirring sounds
> of a mag tape drive starting up, the blinking of lights, etc. are all
> parts of the experience of using vintage computer systems.

Aside from the fact that I seem to need to start the emulator from a boot
or it runs of of memory, I find that M$-Windoze does not seem to interfere
very much even though I dislike admitting that fact. Of course, I also can't
run anything else at the same time.

On the other hand, I use the same 1 GByte ESDI drives on the PC as
on the real PDP-11, each with its own fan to keep it cool. And the front
loading tape drive on the PDP-11 is too heavy by far (even heavier than
an RL02 drive) to lift into the rack, so I will have to have someone help
me take it to the curb. Plus I have not had an occasion to read a 9-track
tape drive for the last 10 years since the TK50 became a viable
distribution media - not that I would EVER consider the TK50 to be
a successful backup drive/media - although a TK70 at 256 MBytes
finally seems acceptable.

> Aye Jerome, surely you don't want to be thought of as an
> anti-classic-computer emulator loving weenie, do you? ;-) After all,
> can it not be said that emulators are, for the most part, preferred by
> weenies who can't lift a PDP-11/44 PSU and are afraid of being shocked
> by one, who can't pop a tall cabinet into the back of a real, not one
> of those little foreign match-box size, station station wagons to haul
> it home, who don't know a screwdriver from an SMD drive cable, or who
> can't even figure out how to disassemble and reassemble a couple of
> linked paperclips?

Well, when you get to be my age (I just turned 63), you may sing a different
tune. This weekend, I just finished nursing a very sore back into a reasonable
disposition after working with a BA23 (NOTE: not the BA123 just the BA23)
system. I had a bad DRV11 (M7941) module that stopped the system from
booting. My first impression was that the PSU might be gone, so I transferred
just the memory to a different BA23 that I hoped was working. That worked
with an M8090, so I added a few more boards including the disk drive. When
all that worked, I transferred back to the original BA23 and it still worked. So
I swapped in the M8192 and the boot ROM board and finally the last 4 dual
boards which ended up crashing the system again. Took out the last 4 dual
boards at which point it was OK and started adding them one at a time.
Viola!!! One board to go - the M7941 and it started crashing again. Out and
replace with an M9047 - bus grant card - AND it works!!!!!! FINALLY!!!!
Anyone have a spare M7941 they want to sell? I also will need those zero
ohm resistors set to a non-standard CSR/VECTOR!!

Plus, I also would like to buy a TU-58 external tape drive - does anyone want
to swap a dozen tapes for an external TU-58 tape drive? I will also consider
buying it.

I also will consider buying a single 4 MByte PMI memory board made by
Christlen. Better still, maybe an 11/93 or an M100 from Mentec. I am
hoping to cure my 7 quad board problem in the BA123 box with the ESDI
hard disk drives. If I can put 8 quad boards into a BA23, then that will
mean that it is the BA123 that is bad. So back to swapping boards again.

Sincerely yours,

Jerome Fine
Received on Sun Jul 29 2001 - 18:04:33 BST