The disclosed embodiments filter out many unnecessary interrogations of the cache directories of processors in a multiprocessor (MP) system, thereby reducing the required size of the buffer invalidation address stack (BIAS) with each associated processor, and increasing the efficiency of each processor by allowing it to access its cache during the machine cycles which in prior MP's had been required for invalidation interrogation. Invalidation interrogation of each remote processor cache directo...

A data processing system includes a memory arrangement comprising a main memory, and a cache memory including a validity bit per storage location to indicate the validity of data stored therein. Cache performance is improved by a special read operation to eliminate storage of data otherwise purged by a replacement scheme. A special read removes cache data after it is read and does not write data read from the main memory into the cache. Additional operations include: normal read, where data is r...

When the access is effected sequentially such as the prefetching of an instruction or the restoration of a register in the stack region, the retrieval is effected simultaneously for the consecutive addresses and the result is stored. When the consecutive addresses are to be accessed, the hit is determined relying upon the result that is stored without effecting the cache memory reference. In the case of mishit, the external memory is readily accessed to shorten the overhead time required for the...

A data processing system having a bus master, a cache, and a memory which is capable of transferring operands in bursts in response to a burst request signal provided by the bus master. The bus master will provide the burst request signal to the memory in order to fill a line in the cache only if there are no valid entries in that cache line. If a requested operand spans two cache lines, the bus master will defer the burst request signal until the end of the transfer of that operand, so that onl...

A data processing system has a bus meter, a memory capable of transferring operands requested by the bus master, and a cache for temporarily storing a selected number of the most recently transferred operands. If the memory provides an operand or a portion thereof which is insufficient in size or alignment to fill a complete entry in a line in the cache, the bus master automatically transfers additional operands adjacent in the memory to the requested operand sufficient to fill that entry.

A computer memory system which includes a relatively slow access main memory unit and a relatively fast access smaller cache memory unit, the memory units being controlled by a central processing unit, and which further includes control circuitry for accessing the cache memory unit for all data words addressed by the central processing unit, and when an addressed word is not available in the cache memory, automatically transferring the addressed word from the main memory to the cache memory, the...

This disclosure describes a snooping coherency protocol for a multiprocessor network wherein every processor has its own private cache and bus interface means and the network is connected via a common system bus. Each processor has its own cache directory and image directory that duplicate each other non-atomically. The snooping protocol utilizes the duality of directories coupled with the non-atomicity of directory updates to maximize processor-cache availability and minimize processor-cache ac...

The invention comprises a system bus apparatus and method for a multi-arm, multiprocessor computer system having a main memory and localized buffer cache memories at each processor. Each block of data in a cache includes tag bits which identifies the condition of the data block in relation to the corresponding data in main memory and other caches. The system bus (SYSBUS) comprises three subparts; 1) a MESSAGE/DATA bus, 2) a REQUEST/GRANT bus and 3) a BCU bus. The MESSAGE/DATA bus is coupled to e...

A computer system includes a processing unit; main storage; cache buffer storage provided between the processing unit and the main storage; and a store buffer device between the processing unit and main storage, receiving data identical to that stored in the cache buffer storage and control information in response to requests from the processing unit and transferring the data and control information to main storage. The transmission from the processing unit to the store buffer device and from th...

Each entry in a cache memory located between a processor and an MMU has two valid bits. One valid bit is associated with the user execution space and the other with the supervisor or operating system execution space. Each collection of valid bits can be cleared in unison independently of the other. This allows supervisor entries in the cache to survive context changes without being purged along with the user entries.