Modifications to the VAX-11/780 microarchitecture to support IEEE floating point arithmetic

Abstract

The VAX-11/780 was designed specifically to implement the VAX architecture. As such, it does not support the IEEE standard for floating point arithmetic. A project was undertaken to provide this support by modifying the 11/780 microarchitecture. Our objective was to produce a microengine that would efficiently execute a modified VAX instruction set, in particular, one that executes VAX floating point instructions consistent with the IEEE standard. We made minimal changes to the 11/780 hardware, relying primarily on changes to the microcode. This paper describes the work of this project.