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The KD11-Z CPU was the CPU of the PDP-11/44; the letter code 'Z' was a tip to the fact that it was the last native UNIBUS PDP-11 CPU, and the last to be made out of discrete chips, and not a microprocessor.

The KD11-Z used the Extended UNIBUS for its bus to main memory, allowing it to have up to 4 mega-bytes of main memory. All devices were attached to a semi-separate UNIBUS (it and the EUB shared data lines, but not address lines); DMA devices could gain access to the memory via a UNIBUS map which connected the two, and mapped UNIBUS addresses to main memory addresses.

Full PDP-11 Memory Management and a cache (the KK11-B) were standard on all KD11-Z's. It also supported the optional FP11-F floating point (full FP11 floating point) and/or the KE44-A Commercial Instruction Set Processor; these plugged into dedicated slots in the CPU backplane (it could work with either, or both).

Hardware Details

The basic KD11-Z CPU consisted of five hex boards:

  • M7094 Data Path module
  • M7095 Control module
  • M7096 Multifunction module
  • M7097 KK11-B Cache module
  • M7098 UNIBUS interface module

In addition, a single dual board, the M7090 Console Interface module, held a number of Berg connector headers used for various input/output functions.

These were placed in a 14-slot CPU-specific backplane, along with the optional FP11-F and KE44-A, and all the main memory cards (the EUB was only present on the main backplane), leaving two slots (one MUD/SPC slot, and one SPC slot, which also contained the 'UNIBUS out').

Board locations are:

Slot A B C D E F
1 M7090 CIM M7091 CIS
2 M7092 CIS
3 M7093 Floating point
4 M7094 Data paths
5 M7095 Control
6 M7096 MFM
7 M7097 Cache
8 M7098 UNIBUS interface
9 M8722 MS11-M
10 M8722 MS11-M (optional)
11 M8722 MS11-M (optional)
12 M8722 MS11-M (optional)

The details of how the EUB and UNIBUS interoperated are not yet clear (it is not covered in DEC's documentation); it was almost certainly similar to that used in the -11/24.

PDP-11/44 setup

The standard mounting box for the CPU was the BA11-A, which is unusual in that it does not use only the standard DEC power distribution connectors; it also provided special connections on bus bars in its power supply, and the KD11-Z backplane uses unique Flexprint cables for power, which go to the special connections (see image).