Editing IBM PL/S (section)

{{Short description|Proprietary IBM systems programming language}}
{{No footnotes|date=April 2010}}
'''PL/S''', short for '''Programming Language/Systems''', is  a "machine-oriented" [[programming language]] based on [[PL/I]]. It was developed by [[IBM]] in the late 1960s, under the name '''Basic Systems Language''' ('''BSL'''), as a replacement for [[assembly language]] on internal software projects; it included support for [[inline assembly]] and explicit control over [[processor register|register]] usage.

Early projects using PL/S were the batch utility, [[IEHMOVE]], and the [[Time Sharing Option]] of [[Multiprogramming with a Variable number of Tasks|MVT]], TSO.

By the 1970s, IBM was rewriting its flagship operating system in PL/S.   Although users frequently asked IBM to release PL/S for their use,  IBM refused, saying that the product was proprietary.   Their concern was that open PL/S would give competitors, [[Amdahl Corporation|Amdahl]], [[Hitachi Data Systems History|Itel]] (National Advanced Systems), [[Storage Technology Corporation]], [[Trilogy Systems]], [[Magnuson Computer Systems]], [[Fujitsu]], [[Hitachi, Ltd.|Hitachi]], and other [[Plug Compatible Manufacturer|PCM]] vendors a competitive advantage. However, even though they refused to make available a compiler, they shipped the PL/S source code to large parts of the OS to customers, many of whom thus became familiar with reading it.

Closed PL/S meant that only IBM could easily modify and enhance the operating system.

PL/S was succeeded by PL/S II, PL/S III and PL/AS (Programming Language/Advanced Systems), and then PL/X (Programming Language/Cross Systems). PL/DS (Programming Language/Distributed Systems) was a closely related language used to develop the [[IBM 8100 DPPX|DPPX]] operating system, and PL/DS II was a port of the S/370 architecture for the DPPX/370 port.

As the market for computers and software shifted away from IBM mainframes and MVS, IBM recanted and has offered the current versions of PL/S to select customers (ISVs through the Developer Partner program.)