The KD11-Z CPU was the CPU of the PDP-11/44; the terminal letter code 'Z' was a tip to the fact that it was the last PDP-11 CPU to be made out of discrete chips, and not a microprocessor, and also nearly the last native UNIBUS CPU (except for the KDF11-U).
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).
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
These were placed in a 14-slot CPU-specific backplane (DEC part number 70-16502 for the complete assembly, 54-13593/50-13592 for the PCB), along with the optional FP11-F and KE44-A, and all the main memory cards (M8722 MS11-M, or later the M8743 MS11-P); the EUB was only present on the main backplane. That left two slots, one MUD/SPC slot, and one SPC slot, which also contained the 'UNIBUS out'.
Board locations are:
|1||M7090 CIM||M7091 CIS|
|3||M7093 Floating point|
|4||M7094 Data paths|
|8||M7098 UNIBUS interface|
|10||main memory (optional)|
|11||main memory (optional)|
|12||main memory (optional)|
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 provided special connections on abus bars in its power supply, and the KD11-Z backplane uses unique Flexprint cables for power, which go to the special connections (see image).