The virtual machine

A parallel computer architecture is proposed that is based on an optimistic style of execution. Specifically, the Virtual Time Machine (VTM) detects violations of data dependence constraints at runtime, and automatically recovers from them. In order to efficiently implement this mechanism, a sophisticated, two-dimensional memory system is proposed that is addressed using both a spatial and a temporal coordinate. Initially targeted for discrete event simulation applications, the long term goal of this work is to develop a general purpose parallel computer that will support a wide range of parallel programming paradigms.This paper outlines the motivations behind the VTM architecture, the underlying computation model, a proposed implementation, and initial performance results. A recurring theme that pervades the entire paper is our contention that existing shared memory and message-base machines do not pay adequate attention to the dimension of time.