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PDP-11/40 with TU56 dual DECtape drive.
Manufacturer: DEC
Year Introduced: January, 1973
Word Size: 16 bits
Physical Address Size: 18 bits
Virtual Address Size: 16 bits
Bus Architecture: UNIBUS

The PDP-11/40, introduced in 1973, was the second machine to support 18-bit main memory addressing on the PDP-11 platform, after the PDP-11/45 (albeit with a subset of the PDP-11 Memory Management architecture). The OEM version of the -11/40 is the PDP-11/35; the machines are completely identical, except for the printing on the front panel inlay.

It used the KD11-A CPU, which connected to the KY11-D front panel via a pair of BC08-R flat cables. Optional additions to the CPU included:

It came in two types of mounting boxes: the 21" BA11-F Mounting Box (usual for the -11/40); and the 10-1/2" BA11-D Mounting Box (early units) and BA11-K Mounting Boxes (later units) (usual for the -11/35).

An -11/40 with a special blue-themed front panel was used as the front end for the KL10 CPU in DECsystem-10s and DECSYSTEM-20s - though the -11/40 panel was hidden behind a cabinet door on the -20.

The 11/40 was also a primary platform for early UNIX.

Configuration changes

A PDP-11/40 setup

Early versions of the BA11-F in the -11/40 omitted the 4 fans at the bottom of the pull-out used to house the CPU, and had only the 5 fans at the top.

The BA11-D used 9-pin DEC power distribution connectors, whereas the BA11-K used the 6-pin/15-pin pair, so presumably the backplane for the BA11-D had a different power harness than the one for the BA11-K (which it is confirmed had the 6/15-pin connectors).

The power harness from the H742 Power Supply was also different in later models, allowing use of an H754 +20V, -5V Regulator which provided +20V, for use with the MM11-U core memory.




The /40 was introduced in January, 1973. It was a higher performance version of the /20, with a microcoded multi-board CPU. 18-bit MMU (-> max. 128 kw memory), FPU and EIS/FIS (extended/floating point instruction set) were available options.

There was a 'graphical' workstation model of the /40, using a VT11 Graphic Display Processor, marketed as the GT44. Many /40s were used in DECsystem-10's (KL10's, to be exact), as the frontend/IO-processor. These were painted differently, the panel looks awsome in blue too. (no, it's not just the frontpanel, that I like about the -11...)

On the picture to the left we can see two RK05's (disk pack drives) and two TU60 (DECcasette) units.

OS's at this point: DOS/BATCH, RSX11, RT-11, RSTS.

Trivia: The 11/40 was one of the most often "cloned" machine. the soviet/tscech/polish SM-4 (CM-4), the hungarian TPA-1140 are all copies of this computer.

See also

External links