A hierarchy of high order languages for systems programming

Abstract

The programming of systems software in higher level languages has been a subject of much interest and debate. At Burroughs the debatability of the issue has long since ceased to exist since both the operating system and the compilers for the B5500 were successfully implemented in variants of ALGOL 60. The low manpower requirements and the ease of maintenance and modification have caused all concerned with the project to accept this approach without question. This technique has the added benefit of producing more reliable software due to the greatly reduced number of lines of code required. When the decision to produce a successor to the B5500 was made, there was no controversy over the use of high level languages but considerable debate over how high a level the languages should be. B5500 ESPOL (Executive System Problem Oriented Language), the operating system implementation language, contained many “unsafe” constructs, for example, the ability to directly address memory through a subscripted reference to an array known, strangely enough, as MEMORY. This allowed coding errors to produce undesirable side effects on the system. Examination of the algorithms used in most operating systems indicated that surprisingly few routines actually require such “unsafe” tools leading to the conclusion that the proper approach to the coding of the overall systems software might be a hierarchical set of systems programming languages with varying degrees of “safety.”