VAX

VAX, standing for Virtual Address eXtension, is a family of 32-bit minicomputers and mainframes developed by Digital Equipment Corporation (DEC) starting in the late 1970s. The VAX line combined a powerful, flexible instruction set with robust system software support, enabling DEC to market machines ranging from desk-sized servers to large multi-user computers. The term VAX also refers to the architecture itself, not only to individual models.

Architecturally, VAX is a 32-bit CISC design with variable-length instructions and an extensive addressing model. It uses a register window mechanism to accelerate procedure calls and provides hardware support for virtual memory via paging. The architecture is generally little-endian and supports a broad set of data types and I/O capabilities. The instruction set emphasizes orthogonality and software compatibility, contributing to a large installed base of operating systems and applications.

VAX systems ran several operating systems, most notably VMS (later known as OpenVMS) from DEC, as well as UNIX variants such as Ultrix and other real-time systems. The combination of reliable hardware, a mature OS, and a wide software ecosystem helped VAX achieve broad deployment in business, academia, and government.

During the 1980s and early 1990s DEC shifted focus toward its RISC-based Alpha line, and traditional VAX hardware began to wane. After DEC was acquired by Compaq and later integrated into HP, production of new VAX-compatible systems declined. However, VAX software and binary assets have remained in use via emulation and through continued support in descendant operating environments such as OpenVMS on newer platforms.