Programming Language I

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What Does Programming Language I Mean?

Programming language I (PL/I) is both a procedural and an imperative programming language that was designed for engineering, scientific and systems programming, and business applications. It has been primarily used by the academic, industrial and commercial sectors since its introduction in the 1960s and is still in active use as of 2011.


PL/1 supports structured programming, recursion, linked lists or linked data structure handling, floating-point, fixed-point and complex character string and bit string handling. The syntax and words used are much like English, and the language is well suited to defining complex data formats using a wide set of functions.

Techopedia Explains Programming Language I

Programming language 1 was born because IBM wanted to design a machine that would supersede all the IBM architectures that came before it to become the common machine architecture for the business and scientific communities. This became the IBM System 360. Before this, programmers had to use different languages to program for each hardware. Similarly, IBM wanted a single common programming language that all users from any field could use.

PL/1 had the following significant language features:

  • 100% free form and does not have reserved keywords
  • Defines data types regardless of hardware
  • A block-oriented programming language that consists of begin blocks, packages and statements. This structuring method allows developers to produce very modular programs and applications.
  • PL/I has control structures. Structures like SELECT…WHEN…OTHERWISE will allow logical operations, while DO statements will allow statements to be executed unconditionally at least once, infinitely, or while a condition is still true or false depending on the need.
  • Supports data structures like arrays, unions, structures, arrays of unions or structures, unions or structures of arrays, and any combination of the above.
  • Has four storage classes: STATIC, BASED, AUTOMATIC and CONTROLLED.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.