The SYSOUT Application Program Interface (SSI function code 79) allows JES to function as a server for applications needing to process SYSOUT data sets residing on JES spool. Use of the SAPI SSI call allows a user-supplied program to access JES SYSOUT data sets independently from the normal JES-provided functions (such as print or network). Users of this function are application programs operating in address spaces external to JES. SAPI supports multiple, concurrent requests from the applications' address spaces. Each issuer of the IEFSSREQ macro is referred to as an "application thread."