Inaccurate descriptions of this elegant high-level language called it "A FORTRAN/COBOL hybrid". Its block structure is reminiscent of ALGOL or even LISP. But sadly, PL/I never caught on the way it should have.
IBM positioned PL/I as a high-level replacement for BAL. Its virtue was that it made the nature of the System/360 hardware visible at the level of the application program; PL/I programs run very fast. This close linkage to the hardware was also its curse; most PL/I programs written for byte-addressable machines (like the Sys/360) couldn't port to other platforms. Other PL/I's, running on machines with an addressability other than to the byte, were functional cripples. So PL/I stayed an IBM-shop specialty item.
But its influence lives on today. One of PL/I's big strengths, the application-level representation of memory addresses, was implemented in the language that eventually became C (and several of its many offspring). And PL/I's comment tokens ("/*" and "*/") are recognized as comment tokens in languages from C to CSS.
Interestingly, the Sperry Corporation so well understood the strength of a language like PL/I that they fostered two languages similar to it: PLUS (Programming Language for Univac Systems) and PLUM (Programming Language for Univac Microprocessors). But PLUS was used only in portions of certain Sperry software products; and although PLUM was offered to end-users, few took advantage of it.
We are expert in PL/I. Call us if this language is still part of your life.