The PDP-12 is a dual-processor 12-bit minicomputer
designed for interactive, real-time laboratory use.
It was introduced in 1969 and 725 were built before
the line was discontinued in 1972.
The basic machine came configured with dual LINCtape drives, a scope display, and IO ports for interfacing with external laboratory equipment.
It can run a number of different operating systems, including DIALPS, LAP6W, and OS/8.
Although you can program the PDP-12 from the front panel, it is
normally used with a terminal attached for user interaction.
Typically this would have been an ASR33 Teletype, but it could
be any current loop or RS232 device.
Some software for the LINC line used the display scope on the PDP-12 for display, and only the input from the terminal keyboard.
|Unlike most tape drives, linctape are random access read/write, so you can have a filesystem on tape and use it interactively like a disk.|
The PDP-12 has special instructions for dealing with real world
devices, since it was designed for lab use. Sampling an analogue
input channel and putting the results in the accumulator is one
instruction. Setting the relays is one instruction. Displaying
a point on the scope is one instruction.
The displays and switches on the front panel are:
INST FIELD - 5 bits
DATA FIELD - 5 bits
RELAYS - 6 bits
INSTRUCTION REGISTER - 12 bits
PROGRAM COUNTER - 12 bits
MEMORY ADDRESS - 12 bits
PROCESSOR STATES - 9 bits
TAPE STATES - 6 bits
TAPE INSTRUCTION - 3 bits
MULTIPLIER QUOTIENT - 12 bits
ACCUMULATOR - 12 bits
MEMORY BUFFER - 12 bits
Left Switches (12)|
Instruction Field (3)
Right Switches (12)|
Start Left Switches
The PDP-12's CPU is constructed out of a large number of small circuit
) each of which performs some very simple, generic
function. The boards are connected together with a custom wire-wrapped
backplane to impliment the architecture of the processor.
The basic PDP-12 configuration includes two 4K core stacks of
The core memory stacks can be seen inbetween rows of flip chips,
a few rows down from the top, next to their W025 driver boards:
This is a
of all the flip chips used in the PDP-12 backplane.