The name VAX refers to its Virtual Address eXtension concept that allowed programs to make use of this newly available memory while still being compatible with unmodified user mode PDP-11 code.

The VAX family ultimately contained ten distinct designs and over 100 individual models in total.

Later versions offloaded the compatibility mode and some of the less used CISC instructions to emulation in the operating system software.

One unusual aspect of the VAX instruction set is the presence of register masks[8] at the start of each subprogram.

On most architectures, it is up to the compiler to produce instructions to save out the needed data, typically using the call stack for temporary storage.

[9] The native VAX operating system is Digital's VAX/VMS (renamed to OpenVMS in 1991 or early 1992 when it was ported to Alpha, modified to comply with POSIX standards, and branded as compliant with XPG4 by the X/Open consortium).

[10] The VAX architecture and VMS operating system were "engineered concurrently" to take maximum advantage of each other, as was the initial implementation of the VAXcluster facility.

Other VAX operating systems have included various releases of Berkeley Software Distribution (BSD) UNIX up to 4.3BSD, Ultrix-32, VAXELN, and Xinu.

[15] The first VAX model sold was the VAX-11/780, which was introduced on October 25, 1977, at the Digital Equipment Corporation's Annual Meeting of Shareholders.

[16] Bill Strecker, C. Gordon Bell's doctoral student at Carnegie Mellon University, was responsible for the architecture.

Through the 1980s, the high-end of the family was continually improved using ever-faster discrete components, an evolution that ended with the introduction of the VAX 9000 in October 1989.

CPU implementations that consisted of multiple MOSFET custom chips included the 8100 and 8200 class machines.

In the MicroVAX I, the ALU and registers were implemented as a single gate-array chip while the rest of the machine control was conventional logic.

This wide range of platforms (mainframe to workstation) using one architecture was unique in the computer industry at that time.

In 1989 DEC introduced a range of workstations and servers that ran Ultrix, the DECstation and DECsystem respectively, using processors from MIPS Computer Systems.

The VAX has four hardware implemented privilege modes: The process status longword contains 32 bits: The first VAX-based system was the VAX-11/780, a member of the VAX-11 family.

The high-end VAX 8600 replaced the VAX-11/780 in October 1984 and was joined by the entry-level MicroVAX minicomputers and the VAXstation workstations in the mid-1980s.

System Industries developed an ability to give more than one DEC CPU, but not at the same time, write access to a shared disk.