Source : Free On-Line Dictionary of Computing

Programming Language/Systems
     
         (PL/S) An {IBM} machine-oriented language derived
        from {PL/I} in the late 1960s for the {IBM 360} and {IBM 370}.
        PL/S permitted {inline} {assembly language} and control over
        {register} usage.
     
        Much of IBM 360 {OS/MFT}(?), {OS/MVT}(?), {OS/VS1} and
        {OS/VS2} ({OS/SVS} and {MVS}) were written in PL/S.  It was
        used internally and never released to the public.  It is
        documented in various IBM internal ZZ-?  publications.
     
        Versions: PLS1, PLSII.
     
        ["PL/S, Programming Language/Systems", W.R. Brittenham, Proc
        GUIDE Intl, GUIDE 34, May 14, 1972, pp. 540-556].
     
        [Were MFT and MVT in PL/S or pure BAL?  Dates?]
     
        (1999-01-24)