PDP-1

PDP-1
Manufacturer:	Digital Equipment Corporation
Year First Shipped:	1960
Form Factor:	small computer
Word Size:	18 bits
Logic Type:	micro-alloy diffused transistor System Modules
Memory Speed:	5 μsec (read/write cycle time)
Physical Address Size:	16 bits (64K words)
Virtual Address Size:	12 bits
Successor(s):	PDP-4
Price:	US$120K (4KW system)

The PDP-1 was the first computer built by Digital Equipment Corporation. It was an 18-bit machine; a load-store architecture, with a single accumulator. Around 50 were built.

The basic PDP-1 included 4KW of core main memory; an optional Type 15 Memory Extension Control allowed (via bank switching) the addition of up to fifteen additional 4KW Type 12 Core Memory Modules, for a maximum total of 64KW.

The later optional Type 10 Automatic Multiply and Divide added instructions to perform multiplication and division at high speed in hardware (previously, they had been done in software subroutines, albeit with support from specialized instructions).

Standard peripherals included a paper tape reader and punch, and a terminal. Optional peripherals included graphics displays, a light pen, line printer, punched card reader and punch, and magnetic tape controller and drives.

A PDP-1 at MIT's RLE served as the nucleus for early hacker culture at MIT, including for the first video game, Spacewar!. The PDP-1/D at BBN was much used in the early ARPANET work; both for software development, and as the Network Control Center's first machine.

Technical details

The instruction format consisted of a 5-bit basic operation code, a 1-bit indirect address bit, and a 12-bit memory address. If the indirect address bit was set in the indirect word, the indirection process repeated. The Program Counter is also 12 bits long.

The base PDP-1 used one's complement arithmetic.

They were built out of DEC's System Building Blocks.

Versions

There were four versions of the PDP-1:

Version	Produced	Comment
PDP-1/A	1, possibly 2*	Prototype, retained at DEC
PDP-1/B	1, possibly 2*	Semi-prototype, sold to BBN
PDP-1/C		Normal production model
PDP-1/D	2?	Custom versions; one each to Stanford and BBN

* = A third prototype, retained at DEC, was produced, but details of it are not known.

The PDP-1/D was a semi-custom machine, and the two that were known to be sold were somewhat different from each other. The basic difference from the regular PDP-1/C was hardware support for time-sharing; support for two's complement arithmetic was also added.

See also

• PDP-1-X

External links

• PDP-1 - Original PDP-1 documents at Bitsavers
• MIT-RLE PDP-1 - material at Bitsavers
• PDP-1 and PDP-3 brochure
• PDP-1 Supplement - focuses on the additional instructions in the -1/D
• A time-shared computer for real-time information processing, 1963
• PDP-1 Manual, 1960
• PDP-1 Manual, 1961
• PDP-1 Manual for I/O (F-25)
• The PDP-1D - includes details on the differences from the -1/C
• PDP-1 Approved Options - covers the -1/D
• PDP-1 Restoration Project - at the CHM
  • Origins of the PDP-1
  • Restoration
• C. Gordon Bell, Gerald Butler, Robert Gray, John E. Mcnamara, Donald Vonada, and Ronald Wilson, The PDP-1 and Other 18-Bit Computers, in C. Gordon Bell, J. Craig Mudge, John. E. McNamara, Computer Engineering: A DEC View of Hardware Systems Design, Digital Press, Bedford, 1978
• Inside Spacewar! (Supplement) - DEC PDP-1 Instruction List - includes the instructions added in the PDP-1/D