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A PDP-11/05 from a sales brochure.

Manufacturer: Digital Equipment Corporation
Architecture: PDP-11
Year Introduced: June 1972
Word Size: 16 bit
Physical Address Size: 18 bits (only 16 bits usable)
Bus Architecture: UNIBUS

The PDP-11/05 was the fourth model in the PDP-11 series, following the PDP-11/20, the PDP-11/45 and the PDP-11/40; it used the KD11-B CPU. It was intended as a cost-reduced low-end machine to replace the PDP-11/20. Like all the other early PDP-11's, it was a UNIBUS machine.

The PDP-11/05 was absolutely identical to the PDP-11/10; the only difference between the /05 and the /10 was the number on the front panel. The /05 was aimed toward the OEM market, while the /10 was intended for end-users. General usage (following DEC's lead) is to refer to all these machines as '11/05's.

The earliest units came in a 5-1/4" box, which had room for only a double system unit backplane. A later version, the /05N and /10N, came in a 10-1/2" BA11-D Mounting Box; the final /05S and /10S versions came in the 10-1/2" BA11-K Mounting Box.

Backplane versions

The PDP-11/05 and /10 came in three versions, with four different versions of the main backplane (the 9-slot system unit holding the two CPU cards).

The original /05 and /10 came with backplanes wired to hold MM11-L 16 Kbyte core memory units. There were two different backplanes: one held two memory units, with one slot left for SPC devices; the other held one memory unit, and provided four SPC slots.

The /05N and /10N had a slightly different backplane, which had space for two MM11-L memory units, but deleted the SPC slot of the previous double MM11-L backplane, and replaced it with a slot to hold the dual-height M9970 console terminal cable board.

The /05S and /10S came with a backplane wired to hold an MM11-U 32 Kbyte core memory, and which provided three SPC slots.


Unlike all the other keyed PDP-11s, which use a circular Ace key, the /05's (and /10s) use a normal flat Yale-type key. The original key is a Chicago Lock Company key, code "GRB 2"; this is cut 215, on a Chicago K5K or Ilco S1041T blank. If simply duplicating an existing key, Hillman Y11 and FR4 blanks may be used (both work, but one has to be trimmed a bit, length-wise).


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