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The PDP-11/04 was a mid/late-70s implementation of the PDP-11 architecture for the UNIBUS; it was a replacement for the PDP-11/05. It was implemented on a single hex card (M7263), the first PDP-11 CPU to be contained on a single board.

It was the first PDP-11 to come standard without a 'proper' lights and switches front panel: the standard KY11-LA Operator's Console front panel had only 'Boot/Init', 'Halt/Cont', and power switches, and the system came with an M9301 ROM card which included a console emulator, which communicated through the console terminal.

DEC did offer the KY11-LB Programmer's Console as an option for the -11/04; it had an octal keypad, the usual 'Halt'/'Start'/etc keys, and a 6-digit LED display which showed address/data digitally.

It came in two chassis configurations: the BA11-L half-height box, which had the entire computer - card guide frame, backplane, power supply, and front panel - sliding into an evil jamming finger-trapping metal sleeve; and a full-height example, basically the same BA11-K box as used throughout the PDP-11 line. (This is very similar to its higher-spec twin, the PDP-11/34.)


Like its predecessor PDP-11/05, the general registers (R0-R5, SP and PC) have addresses assigned to them; they are also accessible from the UNIBUS, and therefore from the KY11-LB Programmer's Console, when the machine is halted. Their addresses are:

Address Register
777700 R0
777705 R5
777706 SP
777707 PC

Note that the registers are word-accessible at odd addresses on the UNIBUS (unlike any other device); and their addresses, like those on the -11/05, increment by 1, not by 2, as is usual for word-sized items.

In addition, four internal CPU registers which record the CPU's most recent memory operations are also available:

Address Register
777710 Source address
777711 Source data
777712 Destination address
777713 Destination data

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