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The KB11-B CPU is the earlier CPU for the PDP-11/70. It is heavily based on the PDP-11/45's KB11-A CPU; the -11/70 is basically an -11/45 with a cache, more main memory, and provision for high/speed I/O device controllers for MASSBUS devices.

Full PDP-11 Memory Management and the cache were standard on all KB11-B's. It used a special 32-bit wide memory bus, the Main Memory Bus, unique to the -11/70, for its bus to main memory; in addition to the speedup of doubling the width, this bus also allowed it to have up to 4 mega-bytes of main memory.

All devices were attached to a separate UNIBUS; DMA devices could gain access to the memory via a UNIBUS map which connected the two, and also mapped UNIBUS addresses to main memory addresses. High-speed devices could be attached to MASSBUS controllers.

The optional FP11-B Floating-Point Processor (full FP11 floating point), and up to four RH70 MASSBUS controllers plugged into the CPU's backplane.


The basic KB11-B consisted of fifteen hex boards:

  • M8130 Data Paths
  • M8131 General Registers and ALU Control
  • M8132 Instruction Register Decode and Condition Codes
  • M8133 ROM and ROM Control
  • M8134 Processor Data and UNIBUS Registers
  • M8135 Trap and Miscellaneous Control
  • M8136 UNIBUS and Console Control
  • M8137 System Address Paths
  • M8138 System Status Registers
  • M8140 System Descriptor amd Console Cables
  • M8141 UNIBUS Map
  • M8142 Cache Control
  • M8143 Cache Address Memory
  • M8144 Cache Data Memory
  • M8145 Cache Data Paths

and a quad board:

  • M8139 Timing Generator

Board sharing

The M8130 through M8139 boards are based on those of the KB11-A CPU of the -11/45; the rest implement the -11/70's extensions (cache - M8142-45, UNIBUS Map - M8141, etc).

In fact, as reported (in the thread below), many of the boards are so similar that the M813x of the KB11-B can be used in place of the M810x of the KB11-A. Comparing an actual M8101 with an M8131, the etch of the former is given as "M8101B" and the latter is given as "M8101 C-P2" (although other M8131's are reported to use the M8101B etch). The traces are mostly identical, but there are a few minor differences.

See also

External links