A multiprocessor digital data processing system comprises a plurality of processing cells arranged in a hierarchy of rings. The system selectively allocates storage and moves exclusive data copies from cell to cell in response to access requests generated by the cells. Routing elements are employed to selectively broadcast data access requests, updates and transfers on the rings.

A multiprocessor system includes first and second microcomputers, a address decoding mechanism, and a ready signalling device. The address decoder is coupled to an address bus, to decode address information transferred by the second microcomputer, and supplies a request signal to a request signal input terminal of the first microcomputer. A bus control unit of the first microcomputer responds to the request signal to detect whether an internal bus of the first microcomputer is free from being used by the CPU, and outputs an acknowledge signal to an acknowledge signal output terminal when the internal bus is free. The ready signaling device is coupled to the acknowledge signal output terminal to supply the ready signal to a ready signal input terminal of the second microcomputer in response to the acknowledge signal outputted at the acknowledge signal output terminal and the request signal. The bus control unit of the first microcomputer further responds to a strobe signal transferred to a strobe signal input terminal through a strobe signal line from the second microcomputer to access an address of the internal memory by using the address information transferred to a set of first address terminals through the address bus and performs a data read/write operation on the address of the internal memory through the internal bus.

A multiprocessor digital data processing system comprises a plurality of processing cells arranged in a hierarchy of rings. The system selectively allocates storage and moves exclusive data copies from cell to cell in response to access requests generated by the cells. Routing elements are employed to selectively broadcast data access requests, updates and transfers on the rings.

A fast path (comprising control and data busses) directly connects between a storage element in a storage hierarchy and a requestor. The fast path (FP) is in parallel with the bus path normally provided through the storage hierarchy between the requestor and the storage element controller. The fast path may bypass intermediate levels in the storage hierarchy. The fast path is used at least for fetch requests from the requestor, since fetch requests have been found to comprise the majority of all storage access requests. System efficiency is significantly increased by using at least one fast path in a system to decrease the peak loads on the normal path. A requestor using the fast path makes each fetch request simultaneously to the fast path and to the normal path in a system controller element (SCE). The request through the fast path gets to the storage element before the same request through the SCE, but may be ignored by the storage element if it is busy. If accepted, the storage element can start its accessing controls sooner for a fast path request, than if the request is received from the normal path. Every request must use SCE controlled cross-interrogate (XI) and storage protect (SP) resources. Fast path request operation requires unique coordination among the XI and SP controls, the SCE priority controls, and by the storage element priority controls. When the accessed data is ready to be sent by the storage element, it can be sent to the requestor faster on the fast path data bus than on the SCE data bus. The fast path data bus may be used to transfer data for requests ignored from the fast path.

A store-in cache memory system for a multiprocessor computer system has a status entry in the cache directory which is RO (read-only) when a line of data is read-only, and thus accessible by all processors on the system, or EX (exclusive) when the line accessible for reading or writing but only by one processor. In addition, each directory has an entry, CH, which is set when data in the line is changed. The cache memory system includes two additional statuses, TEX, or temporary exclusive, and TRO, or temporary read-only. When a data fetch instruction results in a cache-miss, and a line containing the requested data is found in a remote cache with an EX status and with its CH bit set, the line is copied to the requesting cache and assigned a status of TEX. The line of data in the remote cache receives a status of TRO. If a store operation for the data occurs within a short time frame, the status in the requesting cache changes to EX and the line in the remote cache is invalidated. Otherwise, the data in the line is castout to main storage and the status of the line becomes RO in both the requesting and remote caches. The addition of these statuses allows the cache system to assign an exclusive status on an anticipatory basis without incurring penalties when this assignment is not appropriate.