The 5110 I/O Processor And Shared Variables - IBM 5110 User Manual

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THE 5110 I/O PROCESSOR AND SHARED VARIABLES
The 5110 I/O processor is responsible for transferring data from the
active workspace to the tape, the diskette, the display screen, or the
printer, and for transferring data from the tape, the diskette, or the
display screen to the active workspace. Before individual data records
can be transferred by the I/O processor, a shared variable must be
established as the connection between the active workspace and the
I/O processor. That is, the variable is shared between the active
workspace and the I/O processor.
Once this connection is established, the shared variable is used to
send control information and data to the I/O processor and to receive
return codes and data from the I/O processor.