The following account is based on information taken from the Micro/PDP-11 Handbook (EB-24944-18, 1983) and the LSI11 PDP11/03 processor handbook (EB-04870-75, 1975).
In 1970, DIGITAL introduced the first PDP-11, the model PDP-11/20. This was a much more powerful machine than the PDP-8. It was a 16 bit machine with 64KB address space, constructed using small scale integrated circuits, core memory, a hard-wired processor and the UNIBUS backplane/interconnect. The PDP-11/20 was followed by other UNIBUS models which offered variations in price and performance.
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In 1975, the LSI-11 bus was introduced. This extended the range of price/performance tradeoffs. The LSI-11 (later the Q-BUS) was a lower cost version of the UNIBUS, with fewer lines.
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The PDP-11/03 was the first model of this new series of computers. Memory capacity was limited to 64KB, there was only one processor operating mode and only a limited set of floating-point instructions was supported.
in 1979, the second LSI-11 machine, the PDP-11/23, was introduced. This used improved technology to provide increased performance over the PDP-11/03. Memory capacity was increased to 256KB, a second processor operating mode was added and the complete set of floating-point instructions was supported.
The Micro/PDP-11 series of machines was extended with the introduction of increasingly powerful processors, 11/53, 11/73, 11/83 and 11/93. This latter processor had a performance almost equalling that of DIGITAL's standard, the VAX11/780.
Inventory No: 0016
Serial No: AG14737
The PDP-11/03. There were two common processor options, dual height and quad height modules. This example has the LSI-11/2 processor, M7270, a dual height module. Below this are two M8047 CA modules, these are 16KW RAM with two serial lines each. The fourth module is M8029, an RX02 (dual 8" floppy disk) controller.
PDP-11/03 - Modules and the backplane.
Looking straight into the rear of the case and the eight slot backplane.
There are two basic PDP-11/03 processor types, dual height and quad height. However, there are many sub-variants of these two basic types. The quad height module illustrated above is M7264 YA, the KD-11H processor. This has no memory fitted on board. Some variants have 4K words of MOS memory fitted in the space the right of the processor chips. The dual height module is an M7270, the KD11-HA LSI-11 CPU.
PDP-11/03 - Q-Bus Backplane.
The Q-Bus is implimented as a familiar DIGITAL plug-in unit. However, it differs from from, say the OMNIBUS in that the bus only occupies the two leftmost slots (A and B). The slots on the right (C and D) are used for inter-module connection.
PDP-11/03 - Q-Bus Backplane connection details.
The rear of the Q-Bus connector, showing the circuit layout. (The bus is on the right and the 'C-D' interconnect on the left.
PDP-11/03 - Backplane and card-frame.
The unit with the circuit boards removed. This clips onto the base of the computer and the power supply attaches to the backplane to form the front of the computer. Two fans are fitted to the side of this unit to provide cooling air for the modules and for the power supply unit.
PDP-11/03 - Power Supply
The power supply; this provides +5V and +12 volts.