21 Jul
2010
21 Jul
'10
12:46 a.m.
Scott M wrote:
I recently acquired my first DEC PDP. It is a VT103
(VT100 terminal with
a PDP 11/23 inside). It came with a pair of cartridge disk drives (HEAVY!)
that are RK05 compatible, a DEC RX02 (pair of 8" floppy disk drives), boxes
of manuals, 3 DEC operating systems, software, and an extra VT100.
Congratulations. My first PDP-11 was also a VT103 with a DSD 880/8 (5
MB RL01 and RX03)
and 256 KB of memory.
While the DEC operating systems are OK, I am actually
interested in using
the machine to (finally) go through "Lions' Commentary on Unix" (Unix V6),
using software downloaded from http://www.tuhs.org/. (Lions' book here):
http://www.amazon.com/dp/1573980137/
After I do that, I want to move up to Unix v7, 2.9BSD, and try other Unix
distros available for the PDP.
My concern is that the 18-bit PDP 11/23 does not have enough memory.
It currently has 128KB installed, with a maximum of 256K possible after a
memory board upgrade (M8067, MSV11-PK = 256KB). How far do you estimate I
can get with just 128KB memory? Can I get through Lions' book?
I run only RT-11, so I can't help with your questions.
I am looking at adding wires to the backplane to make
it a 22-bit machine,
and using a quad height qbus memory board, M7551 (available in 1MB, 2MB and
4MB sizes). However, I am not ready to dive in and start modifying the qbus
backplane for 22-bit addressing just yet. So my question is:
Rather than invest in a 256KB memory board designed for the 18-bit qbus,
can I install a 22-bit 1MB, 2MB or 4MB memory board in the 18-bit system,
and just use the first 256KB for now? Also, is the VT103 backplane
compatible with a quad-height memory board? (It only has dual-height
cards installed at the present time).
I have had my VT103 enhanced to a 22 bit backplane by adding those extra
4 wires. The
work was done using wire wrap grade wire and stripping the insulation
where the wire had to
be soldered to the backplane. The extra 4 address lines on the VT103
backplane are probably
unused, at least there were on my VT103 backplane.
All of the slots in the backplane are AB / AB which allow them to accept
dual boards.
However, a quad board can also be used, in particular for the CPU and
memory.
If any dual slots are missing, then a bus grant (M9047) is required.
Since the slots
are "serpentine", the order is 1A / 1B / 2B / 2A / 3A / 3B / 4B / 4A.
To confirm, I have used a VT103 with a M8190 CPU, 4 MB of memory, DHV11 and
an RQD11-EC, all quad boards with the last being an ESDI controller.
The disk drives
used a separate PC power supply each with their own fan to keep them cool.
In general, the VT103 power supply is probably on the low side, so it is
probably
best to use as few boards as possible.
Parts inventory:
- VT103, with:
- 4x4 qbus backplane, 18-bit. The manual says "two H803s (2x4 connector
blocks, stacked vertically in a 4x4 configuration)". I know there are
possible issues with "straight" vs. "serpentine" slots, but I have
not
got that figured out yet on the VT103.
- M8186 KDF11-A CPU (Newer revisions of KDF11-A's are 22-bit capable).
http://world.std.com/~mbg/pdp11-field-guide.txt
says: "(Prior to etch rev. C, 18-bit addressing only. ...)"
I could not find revision information on the M8186 board, but "146 CA"
is stamped into one of the red plastic handles. I can email close-up
photos to anyone who wants to take a look and determine if this is a
rev C or later board capable of 22-bit addressing.
- M8043 Quad Serial board. This doc says it is 22-bit compatible:
http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/hardwar…
- M8029 (RXV21) floppy disk board (18-bit DMA only). -Will this be a
problem with Unix v6 or 2.9BSD if running with 22-bit addressing?
- M8208 "VT103 Maintenance Module" (Unknown if 22-bit compatible).
- Xylogics C510 (formerly called "Wizard 1") cartridge disk controller
board, with 18-bit addressing, connected to a pair CDC 9427H "Hawk"
disk drives (one disk drive is DOA, but the other is OK).
- 3rd party memory board (128KB), Christlin Industries, Inc.
So, initially I want to run a 22-bit memory board (M7551) in an 18-bit
VT103 qbus backplane, and access only the first 256KB of memory using
18-bit addressing. Is this possible? Thank you for your help.
I should think it is possible, but I would check with someone who knows.
Jerome Fine