PDP7 Digital Equipment Corporation PDP-7 PDP7
History and Design

Initially conceived as a repackaged PDP-1 with higher module density and faster cycle times, the goals for the PDP-7 range were for a lower cost machine with greater performance than any of the earlier DEC computers. However when consideration was given to the range of PDP-1 and PDP-4 software, an additional goal of PDP-4 compatibility was added to the design.

A sales target of 120 systems(1) was set for the PDP-7 design, more than all of the other computers DEC had built at that time, however it is not known if this target was ever met. Performance was increased with a cycle time drop from 8uS to 1.5uS (limited by the core memory available at that time). Processor, memory and I/O sections were designed around the new B System "Flip Chip" modules, themselves based on earlier 10MHz system modules. Thus the PDP-7 was born, after the first 50 or so systems a design review reworked the I/O systems to use 2MHz R System boards, a design philosophy very much in keeping with the original PDP-1 computer.

Upward program compatibility with the PDP-4 was kept, but using 8-bit ASCII code rather than 5-bit Baudot. The user panel now relocated to the "side" of the cabinet from the "end" configuration of the PDP-4 allowing greater access for servicing. The PDP-7 computer was the first DEC machine to use automatic wire wrapping for production using programs developed on a PDP-4.

Design of the PDP-7 cost less than $100,000, excluding modules and staff costs, from initial concept to first prototype (serial #1). That process only took 9 months, starting in April 1964 with production units delivered in December 1964, the very first production unit going to Bell Labs (serial #3), being hand built by a DEC field service engineer.

Roughly half way through production the PDP-7, the I/O system was reworked to use the lower cost and lower speed R System units, and was re-badged as the PDP-7/A and introduced in 1965. Thoughts then turned to the next computer in the 18-bit range, to be fully auto wired, better specified, have more memory, be cheaper and cure the "dirty" air cooling problems of the PDP-7. Initially called the PDP-7/X, it eventually became known as the PDP-9, the fourth in the range of 18-bit computers and shipped in August 1966.

For a more in depth review of the PDP-7 computer and it's design process, see the 1978 DEC book "Computer Engineering - A DEC view of hardware systems design", by Gordon Bell, Craig Mudge and John McNamara, ISBN 0-932376-00-2.

If you know of any information about any of the PDP-7 systems worldwide, location of existing systems, spare parts, ancillary bits, software, tapes or manuals, then please let us know here. PDP7

 

Close window


  1. Various information on the internet gives sales of the PDP-7 systems as 120 units, however we have not found any information to substantiate this number. From the DEC book "Computer Engineering - A DEC view of hardware systems design", it is apparent that the original sales goal for the PDP-7 range was 120 units. To date the only firm evidence for the number of systems produced is the 18-bit Service list, showing 99 systems. Unless further information surfaces in the future, which is probably unlikely, 99 shipped systems it will have to be.
    (back)