PDP11/45, /50, /55


Operators Console

Switches left to right are :-

Sequential examines or deposits would automatically increment the address pointer, while a deposit/examine cycle would leave the address unchanged. With the halt switch down, pressing continue would step the machine a single instruction or bus cycle.

The lights are as follows (left to right, top to bottom) :-


System Backplane

The large backplane to the left is the CPU. The leftmost two thirds is the FPU and CPU with twisted pair wire-wraps. The slots for the early KB11-A processor left to right are:-

  1. CPU and FPU maintenance slots, KW11 line time clock and bus terminator
  2. M8114 FRH - floating point fraction data path high order
  3. M8115 FRL - floating point fraction data path low order
  4. M8112 FRM - floating point ROM and control
  5. M8113 FXP - floating point exponent data path
  6. M8100 DAP - data paths
  7. M8101 GRA - general registers and ALU control
  8. M8102 IRC - instruction decode and condition codes
  9. M8103 RAC - ROM and ROM control
  10. M8104 PDR - processor data and unibus registers
  11. M8105 TMC - trap and miscellaneous control
  12. M8106 UBC - unibus and console control
  13. M8108 SSR - system status registers (KT-11C)
  14. M8107 SAP or M8116 SJB system address path (KT-11C) or system address buffers
  15. M8109 TIG - timing generator


System Boards

Right to left :-

  • Line time clock (small handle)
  • Four FPU boards
  • Ten CPU boards
  • OEM cache controller on fastbus
  • DL11 serial console card
  • OEM disk controller
  • Two memory cards (128Kb each)


Fastbus Memory Card

This is a fastbus 8Kb MOS memory card. The failure rate for the chips was initially high, and five chips have had to be changed. Early MOS memory did not output TTL voltage levels, and there are a series of level converter chips at the bottom of the card. There is also a controller card required (not shown).


Typical Large System

A typical system would consist of four cabinets containing CPU, expansion for core memory (248Kb), four RK05 disks (2.5Mb each) and a tape drive (TM11+TU10), along with a console terminal (LA36) and line printer (LS-11).

System Components
ComponentWeight (lbs)Power (KW)Boards
CPU+FPU4501.015
Memory3501.032
Disks5600.624
Tape5001.0-
Console1000.2-
Line Printer3400.5-
Totals23004.371

In total, the four cabinets would be eight feet wide and six feet high. In addition to the 5.3Kw of power for the system, an additional 3KW of air conditioning would probably be required.


Processor documentation

Processor Maintenance Manual (link)

Processor block diagrams and microcode flow charts. The tiff files are slightly smaller.

Processor block diagram page 1 of 3 as gif or tiff
Processor block diagram page 2 of 3 as gif or tiff
Processor block diagram page 3 of 3 as gif or tiff
Microcode flow diagram page 1 of 14 as gif or tiff
Microcode flow diagram page 2 of 14 as gif or tiff
Microcode flow diagram page 3 of 14 as gif or tiff
Microcode flow diagram page 4 of 14 as gif or tiff
Microcode flow diagram page 5 of 14 as gif or tiff
Microcode flow diagram page 6 of 14 as gif or tiff
Microcode flow diagram page 7 of 14 as gif or tiff
Microcode flow diagram page 8 of 14 as gif or tiff
Microcode flow diagram page 9 of 14 as gif or tiff
Microcode flow diagram page 10 of 14 as gif or tiff
Microcode flow diagram page 11 of 14 as gif or tiff
Microcode flow diagram page 12 of 14 as gif or tiff
Microcode flow diagram page 13 of 14 as gif or tiff
Microcode flow diagram page 14 of 14 as gif or tiff