ICL Distributed Array Processor

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The Distributed Array Processor (DAP) produced by International Computers Ltd (ICL) was the world's first commercial massively parallel computer. The original paper study was complete in 1972 and building of the prototype began in 1974. The first machine was delivered to Queen Mary College in 1979.

The initial 'Pilot DAP' was designed and implemented by Dr Stewart F Reddaway with the aid of David J Hunt and Peter M Flanders at the ICL Stevenage Labs. Their manager and a major contributor was John K Iliffe who had designed the Basic Language Machine - he is probably better known nowadays for Iliffe vectors.

The ICL DAP had 64x64 single bit processing elements (PEs) with 4096 bits of storage per PE. It was attached to an ICL mainframe and could be used as normal memory. Programs for the DAP were written in DAP FORTRAN which was FORTRAN extended with 64x64 matrix and 64 element vector primitives. It had a Single Instruction Multiple Data (SIMD) architecture. Each operation could be performed under the control of a mask which controlled which elements were affected. Array programs were executed as subroutines of normal mainframe FORTRAN programs and IO was handled by the mainframe.

The design as described in Stewart's 1973 paper is pretty much that which was implemented in the first commercial version except the facility to supply address bits from the processing elements was removed. This change greatly simplified hardware error detection. A notable extra facility was carry propagation to simplify vector mode addition.

The DAP was later hived off as a separate company Active Memory Technology (AMT) which was then taken over by Cambridge Parallel Processors (CPP). It was greatly improved and made much smaller as the Gamma series. An 8-bit processor with some local 8-bit wide memory was added to the processor and fast IO capabilities were implemented. It could be programmed in either C++ or Fortran-Plus. These were much more flexible than DAP FORTRAN, in particular they automatically took care of choosing a mapping from user specified matrix and vector bounds to the underlying hardware.

CPP ceased trading in 2004.