05113514 is referenced by 67 patents and cites 3 patents.

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 every device on the system and is used for transferring messages, data and addresses. The REQUEST/GRANT bus couples between every device on an arm of the system and that arm's bus control unit (BCU). The BCU bus couples between the various BCUs. Both the MESSAGE/DATA bus and the BCU bus include ACK/NACK/HIT bits which are used when responding to messages received over the SYSBUS to inform the message-issuing device if the devices received the message and, if so, the condition of the data in relation to other caches and main memory. The protocol allows inconsistent copies of data to exist and prevents stale data from being used erroneously by monitoring the tag bits and the ACK/NACK/HIT bits. Further, under the appropriate conditions, a copy of the most recent data block may be transferred from one cache to another (with appropriate updating of tags) without updating the main memory. When a memory operation will bring about a situation where cache coherence can no longer be maintained, main memory is updated with the most recent copy of the data and the other caches are either updated or tagged as invalid.

Title
System bus for multiprocessor computer system
Application Number
397124
Publication Number
5113514
Application Date
February 20, 1990
Publication Date
May 12, 1992
Inventor
Michael J Homberg
Grafton
MA, US
John G Faase
Palo Alto
CA, US
John Chang
Morton Grove
IL, US
Brian K Langendorf
Shrewsbury
MA, US
David H Albonesi
Hudson
MA, US
Agent
Wolf Greenfield & Sacks
Assignee
Prime Computer
MA, US
IPC
G06F 13/00
G06F 12/00
View Original Source