on the same machine. In the 1970s, a notable installation of ASP was at Princeton University controlling an IBM 360/91 mainframe. In 1973, IBM rewrote ASP and renamed it JES3, supporting MVS only. Alternatives There was also a JES in OS/VS1 that was often referred to as JES1. In addition, the master (MSTR) subsystem is built into the modern z/OS operating system to start jobs that run outside of the control of JES, including the primary JES itself. Customization Source code was provided to IBM customers for both ASP and HASP, and many customers made substantial enhancements to these programs, some of which were incorporated into the official product. Far more installations made use of HASP than ASP, and in contemporary z/OS systems, there are many more JES2 installations than JES3. Because of their unique history, IBM continues to ship JES2 and JES3 source code instead of object code, unlike most components of the operating system. To improve maintainability and serviceability of user-written enhancements, JES provides a set of exit points that pass control from the JES to user programs at key points of processing. These extensions can provide custom functionality such as special commands, custom print page headings, and non-standard job processing. Current development In 2017, IBM released a statement of direction for JES2 to be the "strategic" JES, meaning that all future development efforts will be focused on JES2 rather than JES3. IBM has reassured customers that JES3 will continue to be supported until an end-of-support date is announced. In February 2019, IBM announced that z/OS 2.5 (expected to be released in 2021) will be the last version of z/OS to include JES3. In October 2019, Phoenix Software International announced that it had licensed the JES3 source code from IBM and would be taking over its maintenance and enhancement. See also System Display and Search Facility (SDSF) most common utility to interact with JES2 Notes References External links IBM mainframe operating systems Job scheduling Remote job entry Assembly language software