The OpenVMS Mixed Pointer Size Environment

Alpha operating system, version 7.0, has vastly increased the amount of virtual address space available for application use. At the same time, fully compatible support for applications that use only 32-bit addresses (also called pointers) has been preserved. An application that mixes 32-bit and 64-bit pointer sizes operates in a mixed pointer size environment. Mixed pointer size applications were the design center for the initial implementation of 64-bit support in the OpenVMS operating system. This paper discusses the reasons why mixing pointer sizes is expected to be a common practice and describes the design of operating system and language features that are provided to ease programming in this mixed pointer size environment.