Digital Equipment Corporation PDP–7/A - S#34

Bell Telephone Labs (USA).

In late 2019 we found compelling research and evidence that machine S#34 is the machine that Ken Thompson and Dennis Ritchie "scrounged" from within Bell Labs and then used it to develop UNIX. In blogs by Warner Losh here and here, Warner dissects the evidence which includes a video, that this PDP–7 S#34 at Bell Telephone Labs is the UNIX research machine. Credit to Warner for this piece of detective work into the origins of UNIX and the role of the PDP–7.

Almost at the same time we found out from Jon Leech and Nathanael Motz that the Paul G. Allen PDPplanet collection at the Living Computer Museum (LCM website), Seattle, had received a donation of PDP–7 S#129 from Fred Yearian, a retired Boeing engineer who had acquired the system many years earlier from Boeing Surplus, and kept it in semi–running condition. Once at LCM it was checked out and repaired, and then used to boot and run UNIX V0, see the two LCM blog articles below –

Restoring UNIX v0 on a PDP–7: A look behind the scenes - November 1, 2019
Unix Version 0 on the PDP–7 at LCM+L - November 13, 2019

The PDP–7 Service list (1972) shows that machine #34 was shipped to Bell Telephone Labs (USA) in January 1969 and consisted of the following options –

Option	S#	Ship	DEC #	Notes
75D	000033	0765	999999	Perforated paper tape punch and control
149B	000039	0765	999999	4K memory upgrade to 8K
177	000025	0765	999999	Extended arithmetic element
340	000020	0765	999999	Precision Incremental CRT Display
342	000012	0765	999999	Symbol generator for 340 display, first 64 characters.
370	000165	0765	999999	Photomultiplier Light Pen
444B	000033	0765	999999	Perforated paper tape reader and control
649	000034	0765	999999	Teletype control
CR01B	000013	1266	018048	Card Reader and Control
PDP7	43	0765	999999	Processor
RC09	000017	0169	048308	Single DECtape transport
76 05477	000001	0169	048308	Custom display ?

For descriptions of the above options see the full PDP–7 options list.

120 PDP–7 and PDP–7/A systems were forecast to be built in total, but the 1972 18–bit service list available (6.5Mb pdf download) only has details of the 99 known PDP–7 and PDP–7/A systems in the list at that time. We do not have any information about the possible remaining 21 systems, who they were delivered to or even if they actually existed.

The PDP–7 appeared to have sold well into Government research and University sectors with 11 systems shipped to the UK alone, almost 10% of the forecast production run! Serial numbers are concurrent for both PDP–7's and the PDP–7/A's, so the missing 21 could be of either type; however we are reasonably confident that the 99 systems shipped were the only ones that were ever built.

If you know of any information about any of the PDP–7 systems worldwide, options, location of existing systems, spare parts, ancillary bits, software, tapes or manuals, then please contact us.

Documents associated with PDP–7 S#34 - (see below)