In this paper we outline some of the technology, successful and unsucc
essful, of part of a large European project in wafer scale integration
(WSI). The work described is an attempt to build a 64 by 64 array pro
cessor on a 4-in wafer. Such a processor would have a computing power
in excess of 10 billion operations per second. A test chip and a demon
stration system, which achieves such a processing power, is also outli
ned.