Electrologica X8
The Electrologica X8 was a digital computer designed as a successor to the Electrologica X1 and manufactured in the Netherlands by Electrologica NV between 1964 and 1968.
Like its predecessor, the X1, the X8 system included core memory, 27-bit word length, and drum memory as secondary storage. The memory address was increased from 15 to 18 bits, for a theoretical maximum memory size of 256k words. The X8 included an independent peripheral processor called CHARON which handled I/O. Other features included up to 48 input/output channels designed for low speed devices such as paper tape, plotters and printers. Unlike the X1, the arithmetic unit of the X8 included floating point arithmetic, with a 41-bit mantissa and 12-bit exponent.
The system is most notable as the target processor for Edsger Dijkstra's implementation of the THE multiprogramming system. This includes the invention of semaphores, enabled by a specific instruction in the X8 instruction set. Semaphores were used not only as a synchronization mechanism within the THE operating system, but also in the request and response data structures for I/O requests processed by the CHARON coprocessor.
