PDP-9

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PDP-9
Manufacturer: Digital Equipment Corporation
Year First Shipped: 1966
Form Factor: minicomputer
Word Size: 18 bits
Logic Type: PNP Transistor FLIP CHIPs
Design Type: microcoded
Memory Speed: 1 μsec
Physical Address Size: 15 bits (32K words)
Virtual Address Size: 13 bits (direct), 15 bits (extended)
Memory Management: bounds register
Predecessor(s): PDP-7
Successor(s): PDP-15
Price: US$30K (8KW system)


The PDP-9 was DEC's fourth 18-bit computer, and the first DEC CPU to use microcode. A little over 400 were built.

Its principal intended use was for real-time systems, including data recording and process control. A variety of models were offered; the basic system provided 8K words of core memory, and the PDP-9/L was a cost-reduced system with cheaper peripherals and 4KW of memory.

Instructions had a 4-bit opcode, 1 bit of indirect, and 13 bits of address. It was a load-store architecture, with a single accumulator. Multiply/divide was a hardware option, the KE09A, which also performed shifting.

Use of more than 8KW of main memory required the Memory Extension Control, KG09A. A memory management option, the KX09A, which included a boundary register to set the boundary between protected and un-protected memory, and two modes for the CPU, was also available.

A large range of peripherals were available, including DECtape (via the TC02 controller), magnetic tape (via the TC59), drum (RM09 controller) and fixed-head disk (RB09).

Further Reading

(All available online through BitSavers.)

  • "PDP-9 User Handbook"