The extensible data facilities of OSL/2, an operating system language, are described. These facilities allow one to create new data types, such as queues, files, and tables, and describe complex access algorithms for these new types. When used in operating system codes, data type extension facilities help the programmer isolate macro and micro levels of complex data manipulation and provide logical places to insert and remove system measurement code. The implementation of these facilities is compatible with existing block structured languages like ALGOL 60 and PL/1 and can be accomplished in a straightforward manner.

The paper outlines the structure of the operating system for the ILLIAC IV, a large array computer being built by the University of Illinois. The system is unique in that it resides primarily on a second control computer and distributes operating system functions among independent programs in a multi-programming, multi-processing mix, where inter-program communication is accomplished by buffer files. The job control language interpreter and hardware interrupt dispatcher are independent modules which may be user defined, invoked dynamically, and co-exist with the standard system modules.