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The PDP-8/M Minicomputer
The PDP-8/M was the OEM version of the PDP-8/F; otherwise, identical, except that
it also came in a "minimal" front panel version.
Introduced in 1972, withdrawn in 1978.
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Compared to an PDP-8/E,
it's in a much shorter box, and has the switching power supply in the back,
whereas the PDP-8/E has the linear power supply down the left side.
The diagram illustrates the difference, the PDP-8/E is on the top,
the 8/M is on the bottom.
The backplane holds 20 cards.
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The first 8/M, purchased in Ottawa back in the late 1990's, has 16k of core and an EAE.
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The second 8/M arrived at the end of May 2006.
It was in rough physical shape, but loaded with cards.
It was manufactured in San German, Puerto Rico, same as
the PDP-8/F in the collection.
The donor was kind enough to give this
writeup of its use.
Restoration is
in progress as of 20060909.
The cards present are as follows (position "1" is at the front of the case):
| Card# | Card | Description |
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| 1 | Front Panel | Front Panel |
| 2 | | |
| 3 |
M8330 | Timing Generator |
| 4 |
M8300 | Major Registers |
| 5 |
M8310 | Major Register Control |
| 6 |
M837 | Extended Memory and Timeshare Control |
| 7 |
M8655 | Terminal Control |
| 8 |
M8650 | Asynchronous Data Control |
| 9 |
M8650 | Asynchronous Data Control |
| 10 |
M847 | MI8E Bootstrap Loader |
| 11 | | Cartfile 20/40 to PDP-8/e Interface |
| 12 |
M849 | RFI Shield |
| 13 |
G111 | Sense Inhibit |
| 14 |
H212 | 8k x 12 Core Plane |
| 15 |
G233 | 8k X-Y |
| 16 |
G111 | Sense Inhibit |
| 17 |
H212 | 8k x 12 Core Plane |
| 18 |
G233 | 8k X-Y |
| 19 |
M847 | 8E Bootstrap Loader |
| 20 |
M8320 | Bus Loads |
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Picture Gallery
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This is the main unit, viewed from the top.
The cards are in the order listed, with the numbers starting at the right.
The front panel is missing, it was shipped separately and isn't in this photo.
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This is the "mass storage" unit for the PDP-8/M as used in the
real-estate office application.
Each of the tapes looks almost like an 8-track tape
(that's what they had before iPods, eh?).
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This is the internal RAM memory of the 8/M.
It's an 8k x 12 bit core plane (and there were two of them in the Maryland system).
Notice that this board has connectors on both the top and bottom.
If you look carefully at the main unit picture (above),
you'll see small "jumper blocks" (for example,
between cards 4 and 5 (the M8300 and
M8310) and others).
The 8/M used an OMNIBus backplane, which meant that the
signals on any given pin were the same for each and every card.
Any special "extra" signals were kludged on top.
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