Dynamic Instruction Scheduling and the Astronautics ZS-1

Reviewer: Lanfranco Lopriore

Smith is a member of the project team for the Astronautics ZS-1. The ZS-1 is a high-speed computer system for scientific applications. It uses two instruction pipelines, one for fixed-point and memory addressing operations, the other for floating-point operations. A salient feature of the ZS-1 pipeline organization is that it reorders instructions at run time (dynamic instruction scheduling). Dynamic scheduling provides better performance and faster compilation than a reordering made by the software at compile time (static instruction scheduling). The paper's contribution is twofold: it accurately identifies the design problems behind pipelining and clearly presents possible implementations of the pipeline concept. The paper is organized into a well-structured set of case analyses, including studies of the CDC 6600, the IBM 360/91, and the ZS-1, whose architecture is described in particular depth. The paper is well written and carefully presented. I recommend it not only for the computer architect involved in a similar project, but also for the nonspecialist who wishes to become acquainted with a primary aspect of high-performance computer organization.