Abstract: In a cache memory setup, a buffer register is provided to accommodate the data read from a data memory. Between the buffer register and the data memory is connected a selector. This selector selectively transfers to the buffer register part of the data read from the data memory. The remaining part of the data is replaced with appropriate data for transfer to the buffer register. This arrangement provides the cache memory with a partial-write function.

Abstract: A main memory is subdivided into a shared region to undergo a write access from a plurality of processors and an input/output device and a plurality of private regions to undergo a write access only from the associated processor. Each of the cache devices includes a region discriminating circuit for determining whether an address generated from the processor is to be employed for an access to the shared region or to the private regions. If the access is to be conducted to the shared region, the cache devices operate according to the write-through method. On the other hand, if the access is to be conducted to the private region, the cache devices operate according to the copy-back method. When the processor or the input/output device rewrites data in the shared region of the main memory, the stored data of the shared region in the cache device of the processor is invalidated.