Converting a Swap-Based System to do Paging in an Architecture Lacking Page-Referenced Bits

Abstract

This paper discusses the modifications made to the UNIX operating system for the VAX-11/780 to convert it from a swap-based segmented system to a paging-based virtual memory system. Of particular interest is that the host machine architecture does not include page-referenced bits. We discuss considerations in the design of page-replacement and load-control policies for such an architecture, and outline current work in modeling the policies employed by the system. We describe our experience with the chosen algorithms based on benchmark-driven studies and production system use.