QIO (Queue I/O) is a term used in several computer operating systems designed by the former Digital Equipment Corporation (DEC) of Maynard, Massachusetts.
I/O operations on these systems are initiated by issuing a QIO call to the kernel. The call returns immediately and if the I/O operation is successfully enqueued, it will be done asynchronously with its completion signaled by the raising of an event flag and—if requested—the issuance of an Asynchronous System Trap (AST) to the calling process/task.
Optionally, the call may be issued as QIOW (Queue I/O and Wait for completion), allowing synchronous I/O. In this case, the wait-for-event-flag operation is combined so the call does not return until the I/O operation completes or fails.
The following operating systems implemented QIO(W):
- RSX-11 (including all of the variants)
- RSTS/E (synchronous only, emulated by the RSX run-time system)
- VMS
Read more about QIO: QIO Arguments in VMS, QIO Completion, Unusual QIOs That Require Complex Processing