QIO
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 was successfully enqueued, it will be done asynchronously with its completion signaled by the raising of an event flag and possibly 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 will be done automatically and the call will not return until the I/O operation has been completed or has failed. QIO calls typically took a partially-standardized list of six parameters known as P1 through P6. These parameters included the I/O opcode (for example, QIO$READ), the I/O buffer starting address, and the I/O bytecount. The remaining three parameters varied with the particular device for which I/O was being enqueued. For example, for a computer terminal, it might be the time to allow for the read to complete whereas, for a disk drive, it might be the starting block number of the transfer. The following operating systems implemented QIO(W): RSX-11 (including all of the variants) RSTS/E VMS
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