ICL Distributed Array Processor facts for kids

The Distributed Array Processor (DAP) was a very important computer. It was made by International Computers Limited (ICL). The DAP was the world's first computer that could do many things at once using a huge number of processors. This is called a massively parallel computer. Ideas for the DAP started in 1972. Building a test version began in 1974. The first DAP computer was delivered to Queen Mary College in 1979.

How the DAP Was Made

The first test version, called the 'Pilot DAP', was designed by Dr Stewart F Reddaway. He worked with David J Hunt and Peter M Flanders at ICL's labs in Stevenage. Their manager, John K Iliffe, also helped a lot. He is known for something called Iliffe vectors.

The ICL DAP had 64x64 tiny processors. These are called processing elements (PEs). Each PE had 4096 bits of memory. The DAP was connected to a larger ICL computer, called a ICL mainframe. The DAP's memory was part of the mainframe's memory.

Programs for the DAP were written in a special language called DAP FORTRAN. This was like the regular FORTRAN language. But it had extra commands for working with 64x64 grids (matrices) and lists (vectors) of 64 numbers. DAP Fortran programs were turned into a simpler language called APAL. This stands for Array Processor Assembly Language.

The DAP used a special way of working called single instruction, multiple data (SIMD). This means one instruction (command) could control many processors at the same time. You could also use a "mask" to choose which processors would follow the command. Programs for the DAP ran as small parts of bigger mainframe programs. The mainframe handled things like saving and loading data.

Moving data into and out of the DAP took some time. Also, if a problem didn't fit the 64x64 grid perfectly, it was harder to solve. For example, a 65x65 problem was tricky. But for problems that fit the DAP's design, it was incredibly fast. It could be 100 times faster than other powerful computers of its time, like the Cray machines. The ICL 2980 mainframe wasn't very popular. This limited how much the DAP could be used at first.

The original design from 1973 was mostly kept for the first commercial DAP. One change was removing a feature that let processors supply address bits. This made it easier to find hardware errors. Another helpful addition was a way to speed up adding numbers in vector mode.

What Happened After ICL

The DAP project was later sold to a new company called Active Memory Technology (AMT). This company was then bought by Cambridge Parallel Processors (CPP). They made the DAP even better, smaller, and faster. These improved versions were called the Gamma series.

They added an 8-bit processor to each PE. This processor also had its own small, fast memory. The new DAPs could also handle data input and output much faster. You could program these newer DAPs using C++ or Fortran-Plus. These languages were more flexible than DAP FORTRAN. They could automatically figure out how to arrange your data to fit the hardware.

Some DAPs are now kept at the Computer History Museum. CPP stopped doing business in 2004.

Mini-DAP and Mil-DAP

A smaller version of the DAP was made between 1984 and 1987. This one had 32x32 processors instead of 64x64. The commercial version was called the Mini-DAP. It was usually connected to a PERQ computer, so it was sometimes called the PERQ-DAP. A tougher version for military use was called the Mil-DAP.

See also

• Connection Machine
• Goodyear MPP
• MasPar
• Parsytec
• SUPRENUM