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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 Introduced in 1972, withdrawn in 1978.

Comparison of PDP8-8/E amd PDP-8/M cabinet sizes S M L XL 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.

The first 8/M, purchased in Ottawa back in the late 1990's, has 16k of core and an EAE.

Restoration of the second 8/M

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):
1Front PanelFront Panel
3 M8330Timing Generator
4 M8300Major Registers
5 M8310Major Register Control
6 M837Extended Memory and Timeshare Control
7 M8655Terminal Control
8 M8650Asynchronous Data Control
9 M8650Asynchronous Data Control
10 M847MI8E Bootstrap Loader
11Cartfile 20/40 to PDP-8/e Interface
12 M849RFI Shield
13 G111Sense Inhibit
14 H2128k x 12 Core Plane
15 G2338k X-Y
16 G111Sense Inhibit
17 H2128k x 12 Core Plane
18 G2338k X-Y
19 M8478E Bootstrap Loader
20 M8320Bus Loads

Picture Gallery

PDP-8/M number 2 S M L XL 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.
The Cartrifile Tape Cartridge System S M L XL 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?).
An 8k x 12 Core Plane from the PDP-8/M S M L XL 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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