IBM System/36 - Spooling (printing)

Spooling (printing)

SPOOL is an acronym for Simultaneous Peripheral Operations On Line.

As with some modern machines, computer printers made during the S/36 era were very slow, to the point that it was possible for the S/36 or other computers to write data to the printer faster than it can print. Spooling was used on the S/36 to deal with this issue, with the added benefit that multiple programs could write to the printer concurrently, without waiting for each other to finish.

To allow the system to manage the problem, system components called "writers" and "spool files" were developed. A writer is a small system program that reads the spool file, matches a particular printer with a ready-to-print spool object, and begins sending instructions to the printer. It's a two-way process; the printer sends a signal back to the system when it is ready for more work. In order to avoid mixing up data from two spool files, the first report to finish and close is traditionally printed first.