The Mil-DAP preservation – CCS Working Party conclusion

The Distributed Array Processor (DAP), developed at Stevenage by the Research and Advanced Development Centre of ICL, was one of the first - or possibly indeed the very first - successful examples of parallel processing hardware. It consisted of an array of 1024 interconnected processors operating in parallel upon a single input data stream.

A DAP product was developed and built by ICL, and was delivered on 2900 Series mainframes in 1978. With advances in integrated circuit technology smaller versions became possible. The Mil-DAP was the militarised version of the DAP technology, incorporating ruggedised construction and shielding against electronic interference.

That the DAP was seen as being technologically significant is amply illustrated by its being given The Queen's Award for Technology.

As an illustration of the power of DAP take the example of a weekly run in which a set of six 6-bit numbers (plus a bonus seventh number) in the range 1 to 49 have to be compared against several million such sets of seven numbers. When first introduced, the weekly run was taking some two hours on a DEC mainframe. CAFS would have completed the search in about two minutes. It would have been nice to be able to say that DAP would have taken two seconds. Unfortunately, this is not the case - DAP would take about a quarter of a second!

The CCS Mil-DAP Working Party, led by Brian Russell and based in Manchester, attempted to restore a surviving Mil-DAP and the associated PERQ workstation, and had considerable success during three years of work. Unfortunately it was difficult to find a replacement for a vital missing board: one of the eight array boards. They eventually found two boards, but both were later revisions than the missing board and both had been 'museum exhibits' and therefore were probably non-functional. More serious was a total lack of software, particularly the basic operating system and device drivers needed to run the machine. The hardware was consigned to secure storage at The Science Museum and the Working Party has been formally closed down.

For a report on the work done see Resurrection Issue 34, page3.

Parallel processing is now being built into microprocessors and PC’s. It would be good to have more on the original DAP developments – either as links to good material already on the web or as a writeup from one of the people involved at the time.

Note there is more information about the DAP in this Wikipedia entry - click here to view.