MIMD architectures became popular when progress in integrated circuit technology made it possible to produce microprocessors which were relatively easy and economical to connect into a multiple processor system. In the early eighties small systems, incorporating only tens of processors were typical. The apperance of Transputer in the mid-eighties caused a great breakthrough in the spread of MIMD parallel computers and even more resulted in the general acceptance of parallel processing as the technology of future computers. By the end of eighties mid-scale MIMD computers containing several hundreds of processors become generally available. The current generation of MIMD computers aim at the range of massively parallel systems containing over 1000 processors. These systems are often called scalable parallel computers.