Abstract: A multi-user system for managing a database, and comprising a file access processor and a plurality of application support processors. The file access processor is provided to access the database, and the support processors are connected to the file access processor to read and update data objects in the database. The file access processor includes a locking system to lock data objects for selected support processors to limit access to locked data objects by the other support processors. This locking system includes an implicit locking subsystem to place implicit locks on data objects automatically in response to receiving processing requests from the support processors, and an explicit locking subsystem to place explicit locks on data objects in response to receiving explicit locking requests from the support processors. The explicit locks are integrated into the locking scheme in a manner minimizing lock conflicts.

Abstract: A method for increasing cache concurrency in a multiprocessor system. In a multiprocessor system having a plurality of processors each having a local cache in order to increase concurrency the directory entry for a line in local cache will be assigned an LCH bit for locally changed status. If the last cache to hold the line had made a change to it this bit will be set on. If not, the bit will be off and thereby allow the receiving or requesting cache to make change to the line without requiring a main storage castout.

Abstract: A computer having a plurality of plug-in modules is provided with a holding circuit for transmitting an interrupt signal over an interrupt signal line. The holding circuit conducts the interrupt signal in the appropriate manner regardless of whether or not a given module is plugged in. At the same time it ensures that a plugged-in module responds to the interrupt signal in the appropriate manner.