IBM PL/S

PL/S, short for Programming Language/Systems, is a "machine-oriented" <a href="/facts/Programming_language/cWTYbgWa">programming language</a> based on <a href="/facts/PL%2fI/469mVYgd">PL/I</a>. It was developed by <a href="/facts/IBM/QszA7nwd">IBM</a> in the late 1960s, under the name Basic Systems Language (BSL), as a replacement for <a href="/facts/Assembly_language/7XuV0cla">assembly language</a> on internal software projects; it included support for <a href="/facts/Inline_assembly/Dn60Jm44">inline assembly</a> and explicit control over <a href="/facts/Processor_register/32RvbUdz">register</a> usage.
Early projects using PL/S were the batch utility, <a href="/facts/IEHMOVE/d0kWFFAf">IEHMOVE</a>, and the <a href="/facts/Time_Sharing_Option/1jQFtL1r">Time Sharing Option</a> of <a href="/facts/Multiprogramming_with_a_Variable_number_of_Tasks/nQbdNbx6">MVT</a>, 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, <a href="/facts/Amdahl_Corporation/oCbmoP1z">Amdahl</a>, <a href="/facts/Hitachi_Data_Systems_History/qYvQecjX">Itel</a> (National Advanced Systems), <a href="/facts/Storage_Technology_Corporation/Cru6d1xs">Storage Technology Corporation</a>, <a href="/facts/Trilogy_Systems/1aeW3vfv">Trilogy Systems</a>, <a href="/facts/Magnuson_Computer_Systems/7WX5Aenr">Magnuson Computer Systems</a>, <a href="/facts/Fujitsu/6e5gvNSa">Fujitsu</a>, <a href="/facts/Hitachi%2c_Ltd./KeK38e82">Hitachi</a>, and other <a href="/facts/Plug_Compatible_Manufacturer/TKayPudG">PCM</a> 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 <a href="/facts/IBM_8100_DPPX/lILTrBvN">DPPX</a> 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.)

IBM PL/S open-in-new

IBM PL/S