This is the 1st Digital pdp11/05 in our collection. The pdp11/05 is a 16-Bit Unibus system, introduced in June 1972. This unit is dated 21st February 1974 and has serial number 6491. The pdp11/05 came in two case sizes. This one is in the smaller case designed to be low-profile. Our 2nd pdp11/05 uses the larger case.

The label states this machine has:

MM11L Memory, 16k on UNIBUS which uses:
G110 – Hex format memory control logic and data channels
H231 – Hex format memory driver logic
H214 – Quad format core stack

KD11B Processor on two boards:
M7260
M7261

The Processor board uses four 74181 ALU’s, Although these ALU’s are purpose-built processors on a chip, they are not a full Microprocessor. The chip is only a ALU, and lacks any accumulators, buffers, address control or data control. All these parts had to be external to the IC. A 74182 look-ahead carry generator was required to bit-slice several 74181 ALU’s together, allowing the 16-bit Processor to run from four 4-bit ALU’s.

The Processor clock is set to 155ns. This gives 6.45MHz. The throughput of the CPU however is significantly less due to the CPU architecture. This was prescaled to allow Serial baud rates of 2400, 1200, 600, 300 and 150. The ASR33 Teletype ran at 150cps.