Abstract: In a semiconductor memory disk apparatus, when a read command is input as an input/output request during a restore operation, if a flag in a directory memory corresponding to the requested block is not set, data in a requested block is read out from a backup unit, and is written in the corresponding block of a semiconductor memory. At the same time, the readout data is transferred to a designated destination. Thereafter, the flag in the directory memory corresponding to the requested block is set. However, if the flag in the directory memory corresponding to the requested block is set, the requested data is read out from the semiconductor memory, and is transferred. When a write command is input as the input/output request during a restore operation, the data is written in a designated block of the semiconductor memory and the same data is also written in the corresponding block of the backup unit. In this case, the flag in the directory memory corresponding to the requested block is set.

Abstract: A request buffer apparatus controls a plurality of access requests to devices to be accessed (e.g., memory banks) commonly used by a plurality of accessing devices (e.g., a CPU, channels, and DMA units) in a data processing system. The apparatus has a request buffer means which has a plurality of buffers for storing the access requests. Write/read operations of the requests in and from the request buffer means are randomly performed in accordance with the status of the device to be accessed corresponding to the request stored in the buffer. Requests corresponding to the same device to be accessed are written in the empty buffers of the request buffer means in the order they are generated, and are read out from the request buffer means in the order that they are written. Each device to be accessed has a buffer write address generating means, and the buffer write status of each buffer is indicated so as to obtain the next buffer write address.

Abstract: A data prefetch apparatus provided between a main memory formed of a plurality of memory blocks and an I/O device whose data transfer speed is slower than that of the main memory, comprising an address counter for the main memory and a data buffer for storing the data prefetched from the main memory. In the data prefetch apparatus, a full/empty detector is connected to the data buffer and a memory block detector is connected to the address counter and the data prefetch is interrupted when the over-access of the one of the memory block is detected and is restarted when the data buffer is empty and data request is supplied from the I/O device.

Abstract: A DMA bus load varying unit applied to a data processing system has a DMA bus and a memory connected to the DMA bus is provided with a mode designating circuit for designating a memory read and write operation, a continuous operation of the memory read and write operation, and a start and stop operation of the memory read and write operation for the memory, a clock-pulse generator connected to said mode-designating circuit, a period counter connected to the clock-pulse generator for counting clock-pulse signals from the clock-pulse generator, a period-setting circuit for specifying an arbitrary period, a first comparator for comparing the output from the period counter with the output from the period-setting circuit and for producing a first coincident signal when they are equal, a flip-flop connected to the first comparator for producing the DMA bus request signal in accordance with the coincident signal; DMA bus circuit connected to the mode-designating circuit and the flip-flop which is triggered by the DM