VAX was a 32-bit CISC computing architecture developed in the mid-1970s by Digital Equipment Corporation (DEC). VAX was an acronym for Virtual Address eXtension, and it was in fact one of the first computer systems designed to support virtual memory.
Early VAX computers were quite large systems as they were implemented in TTL technology, a single CPU consisted of a complete rack and the complete system occupied an entire room. Following VAX generations were already smaller, and finally the MicroVAX emulated most of the instruction set to dramatically reduce the required number of hardware. Later versions of the MicroVAX were finally able to offer an entire CPU on a VAX microprocessor, which also allowed to build VAX-based workstations.
In the late 1980s RISC technology became more and more popular, and in 1992 DEC introduced their own 64-bit RISC microprocessor, the Alpha AXP which was capable of running OpenVMS and soon replaced the traditional VAX hardware.
After DEC got into financial trouble they were purchased by Compaq, which then cancelled the VAX project. Compaq was purchased by Hewlett-Packard and we all know how this ended: the Alpha AXP and all related technology was cancelled, along with OpenVMS.
Nevertheless there's still a large number of VAX systems in use today and many experts still consider OpenVMS to be one of the most reliable operating systems ever created.