ILLIAC IV - Solomon

Westinghouse explored the latter solution in a project known as Solomon. Since the highest performing computers were being used primarily for math processing in science and engineering, they decided to focus their CPU design on math alone. They designed a system in which the instruction stream was fetched and decoded by a single CPU, the "control unit" or CU. The CU was attached to an array of processors built to handle floating point math only, the "processing element"s, or PEs. Since much of the complexity of a CPU is due to the instruction fetching and decoding process, Solomon's PEs ended up being much simpler than the CU, so many of them could be built without driving up the price. Modern microprocessor designs are quite similar to this layout in general terms, with a single instruction decoder feeding a number of subunits dedicated to processing certain types of data. Where Solomon differed from modern designs was in the number of subunits; a modern CPU might have three or four integer units and a similar number of floating point, in Solomon there were 256 PE's, all dedicated to floating point.

Solomon would read instructions from memory, decode them, and then hand them off to the PE's for processing. Each PE had its own memory for holding operands and results, the PE Memory module, or PEM. The CU could access the entire memory via a dedicated memory bus, whereas the PE's could only access their own PEM. Although there are problems, known as embarrassingly parallel, that can be handled by entirely independent units, these problems are generally rare. To allow results from one PE to be used as inputs in another, a separate network connected each PE to its eight closest neighbors. Similar arrangements were common on massively parallel machines in the 1980s.

Unlike modern designs, Solomon's PEs could only run a single instruction at a time, and every PE had to be running the same instruction. That means the system was only useful when working on data sets that had "wide" arrays that could be spread out over the PEs. These sorts of problems are not uncommon in scientific processing, and are very common today when working with multimedia data. The concept of applying a single instruction to a large number of data elements at once is now common to most microprocessor designs, where it is referred to as SIMD, for "Single Instruction, Multiple Data". In Solomon, the CU would normally load up the PEMs with data, scatter the instructions across the PEMs, and then start feeding the instructions to the PE's, one at every clock cycle.

Under a contract from the US Air Force's RADC research arm, they had built a breadboard prototype machine in 1964, but the RADC contract ended and Westinghouse decided not to follow it up on their own.