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Manufacturer: Digital Equipment Corporation
Year Introduced: September, 1963
Form Factor: minicomputer
Word Size: 12 bits
Logic Type: transistor System Modules
Instruction Speed: 18 μsec (addition)
30 μsec (subtraction)
Memory Speed: 6 μsec (cycle time)
Physical Address Size: 15 bits (with Memory Extension Control; 32K words)
Virtual Address Size: 12 bits (direct), 15 bits (extended)
Predecessor(s): none
Successor(s): PDP-8
Price: US$25.8K (CPU and 4KW of memory)

The PDP-5 was DEC's first 12-bit computer, the predecessor to the PDP-8; in some sense, it was DEC's first minicomputer (although the -5 pre-dated the creation of that term). Like the -8, it was a load-store architecture; its instruction set was very similar to that of the -8. A Type 154 Memory Extension Control unit was added later, to support bank switching, and thus allow the use of more than 4KW of main memory.

It was constructed out of the standard modules created for the PDP-4. It was built using the bit-slice concept, where one bit of all the registers and the data paths between them was implemented on a single PCB; a number of these boards (equal to the word length of the machine) formed the CPU. To minimize the initial basic cost, it had an I/O bus, rather than the radial links from the CPU to individual peripherals used in all earlier DEC machines, such as the 18-bit machines like the PDP-1.

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