Abstract: A highly reliable computer system is intended to duplicate processors, compare the outputs of the processors with each other and enhance the validity of the output of processor system. If a mismatch between the outputs is detected, one of the processors performs a process of saving an internal state of the processor in amain memory and diagnosing factor of the detected mismatch. If the process is recognized to be continued in a duplex mode, the processors are re-synchronized by a processor reset, and initialize themselves and restore the internal information saved in the main memory for continuing the process having been proceeded before the fault occurred.

Abstract: A computer memory system is disclosed with an input/output circuitry capable of separating the load separating the load capacitance of an output circuit of a semiconductor memory connected to a memory bus from the memory bus. In order to separate the load capacitance of a semiconductor memory connected to a memory bus signal line, a Schottky diode is arranged between the semiconductor memory and the memory bus line, and a voltage control circuit is provided to control whether a reverse bias voltage is applied to the Schottky diode. The speed of signal transmission does not decrease even when a large number of semiconductor memories are connected to the memory bus since the load capacitance of the semiconductor memories is separated from the bus. Therefore, it is possible to construct a high speed and large capacity memory system.

Abstract: A multiplication, division and square root extraction apparatus which calculates the solutions to addition, division and square root extraction functions by approximation using iteration has a multiplier, an adder-subtracter and a shifter of prescribed bit width connected to a bus. Iteration is conducted by inputting the output of the multiplier to the adder-subtracter or the shifter and returning the result to the input of the multiplier via the bus. A shifter and an arithmetic and logic unit connected to a second bus connected to the aforesaid bus via a switch have a greater bit width than the prescribed bit width and are used for large scale calculations, thus preventing a reduction in processing speed.

Abstract: A prefetch buffer adapted to be installed between a cache memory and a main memory in a computer system having a CPU. The prefetch buffer includes a buffer storage having at least one entry for storing prefetched data and an address tag, which is to be used for searching the data, as a pair; a data searcher for searching, from the data stored in the buffer storage, for data having an address requested by the CPU; and an address estimator for determining an address of data to be prefetched next from the main memory, based on the address requested by the CPU and also on a history of the addresses of data prefetched in the past from the main memory; and an address generator for generating an address of data to be prefetched from the main memory. With this arrangement, it is possible to improve the hit ratio of the prefetch buffer regardless of the direction in which the access address varies.

Abstract: A multiplication, division and square root extraction apparatus which calculates the solutions to addition, division and square root extraction functions by approximation using iteration has a multiplier, an adder-subtracter and a shifter of prescribed bit width connected to a bus. Iteration is conducted by inputting the output of the multiplier to the adder-subtracter or the shifter and returning the result to the input of the multiplier via the bus. A shifter and an arithmetic and logic unit connected to a second bus connected to the aforesaid bus via a switch have a greater bit width than the prescribed bit width and are used for large scale calculations, thus preventing a reduction in processing speed.