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System overview of the Application System/400

 Award plaque by D. L. Schleicher
and R. L. Taylor

This paper describes IBM's recently available general-purpose midrange computers—the Application System/400™, the basic intentions of the product, the significant factors setting forth system requirements, the primary design themes incorporated in the implementation of those requirements, and a description of some of the key system components. However, the paper is not intended to provide a complete system description.

Originally published:

IBM Systems Journal, Volume 28, Issue 3, pp. 360-375 (1989).

Significance:

The IBM AS/400®, the precursor of today's iSeries™ computers, was an object-based system with an integrated DB2® database, designed to implement E. F Codd's relational database model. Codd created the revolutionary relational model for database management while working at IBM.

This paper describes the machine interface and layered hardware and software architecture of the AS/400. This architecture facilitated the transition from complex instruction set computing (CISC) architecture to the PowerPC™ reduced instruction set computing (RISC) architecture without requiring that the applications be recompiled. The AS/400 also introduced the single-level store, whereby programmers were relieved from keeping track of where their data resided, and the data was made to appear as if it were stored in a single location.

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