Master File Directory,
MFD.
always synchronous. Disk and tape
instruction,
necessary error recovery. Control is not returned to
operation is complete, except for tape rewind or rewind and unload
operations, which return control
started. No interruption is ever received as the result of
Input/output operations to a card reader, card punch, or printer are
initiated via a
operation,
received frem the started device. Because the
end-of-file, or forms overflow.
or asynchronous.
program may wait for all terminal input/output operations to complete
synchronous but a user
attention key.
actual
take place.
synchronization processing for
overall flow of control for
2-94 IBM