Feb 072014

Fresh off the truck comes this exciting eBay find: A Digital Equipment Corp. (DEC) PDP-8/M! According to the seller, this particular machine originally controlled some sort of industrial sewing machine. The board numbers tell me that it should have 8192 words (12 bits each) of core memory. I’ll mate it up with my recently-acquired Teletype Model 33 ASR (commonly but incorrectly called an "ASR-33") which will provide a printing terminal with low-speed paper tape reader and punch.

It didn’t come with its power key, but I have a new one on the way from a collector in Canada who had several of them made by a locksmith. Luckily the keyswitch is turned on already. I’ve applied power to the machine and found that it’s semi-functional but not working correctly yet. I’ll need to do some work on this machine, but it’s reassuring to me that it is showing some reasonable signs of life. The seller bolted the machine to a piece of plywood to help keep the machine centered in the shipping carton, and that helped protect the delicate front panel switches.

(Update, 2013-02-08) The seller sent me a scanned image of a manual cover to show me what my new PDP-8/M came out of. It was part of an Automatic Controlled Stitcher Model A by USM Corporation, United Machinery Group. He also says he’s sending me a key for the machine, and he has some spare boards that I’ll probably be interested in buying.

It came with these boards installed, from front to rear:

Slot Card Number Description
1 ? Programmer’s panel (toggle switches and LEDs)
2 M8330 KK8-E CPU, CPU timing generator
3 M8310 KK8-E CPU, CPU major registers control
4 M8300 KK8-E CPU, CPU major registers
5 (none) (empty)
6 Y083 Cassette timing board for Sykws TT100 tape drive
7 (none) (empty)
8 Y084 Cassette device selector for Sykes TT100 tape drive
9 Device 50 I/O Card Unknown; probably a custom interface card?
10 Device 51 I/O Card Unknown; probably a custom interface card?
11 (none) (empty)
12 (none) (empty)
13 Y111 Encoder interface board (?)
14 M8650 KL8-E Teletype control
15 M837 KM8-E/MC8-E, Memory extension and time share
16 M849 KK8-E CPU, Memory shield
17 G111 MM8-EJ Core sense/inhibit (part of H212)
18 H212 MM8-EJ Core memory 8k stack
19 G233 MM8-EJ Core x-y drives 8k (part of H212)
20 M8320 KK8-E CPU, Omnibus loads (bus terminator)