SYSIN

In OS/360, System Input (SYSIN) datasets are spooled direct-access storage device (DASD) data sets managed by the operating system. They are spooled by system readers, which typically read from card readers, although they can also read from magnetic tape. The support in OS/VS2 R1 (SVS) is essentially the same. The programs Attached Support Processor (ASP) and Houston Automatic Spooling Priority (HASP){{cite book | section-url = http://www.bitsavers.org/pdf/ibm/370/hasp/GC27-0052-0_HASP_II_Version_4_Users_Guide_Sep76.pdf#page=20 | access-date = August 1, 2025 usurp the spooling functions of OS/360 and SVS, maintaining SYSIN datasets with their own SPOOL mechanisms.

In OS/VS1, SYSIN datasets are managed by Job Entry Subsystem 1 (JES1), retaining many of the same operator commands but replacing the SPOOL mechanism.

In MVS, OS/VS2 R2 and later, SYSIN datasets are managed by a Job Entry Subsystem (JES2 or JES3), retaining many of the HASP or ASP operator commands and providing their own SPOOL mechanisms.

SYSIN also refers to and JCL statements, and many programs expect an allocation with ddname SYSIN.

DOS does not support spooling, but several spooling programs are available for it, e.g., Grasp, POWER.