Method to test and set data in a record on disk in one atomic input/output operation.

摘要

An I/O Test and Set operation is provided for testing and changing data, e.g. flags in an access status record on DASD in one atomic I/O operation, which uses a string of standard Channel Command Words like Read, Write, Seek and Search in combination with additional records on DASD, containing the test and set values to be used by the Channel Command Word string. The I/O Test and Set operation is used in a Shared Disk Facility, in a flagging protocol for avoiding simultaneous and conflicting accesses from independent computer systems having access to the same physical DASD, thus realizing a disk sharing system at user or minidisk level.