VAX (Virtual Address eXtension) was a once famous computer produced by Digital Equipment Corporation (a now defunct computer company, founded in 1957 by Ken Olsen, rich uncle of the Olsen twins). The term "VAX" was understood to be an acronym for Virtual Address (sound of throat clearing); or perhaps Visual Analysis (garbled); or, according to one junior Marketing Manager, Very Amiable Xylophone. The last of these is considered the least likely; and the manager who suggested it was the butt of the second greatest insult ever delivered at DEC when Ken Olsen, Chairman, President, and CEO looked him in the eye and said You and I have a lot in common - we've both risen about as far as we're going to in this company.
There is also a vacuum cleaner manufacturer called Vax, which now inspires the famous joke:
Nothing sucks like a VAX!
The VAX architecture and instruction set have its origins in the Soviet Union. In the 1950s during the Korean War, a Russian experimental warplane flew into South Korean airspace and was subsequently shot down. In the crash remains, there was a sophisticated tube-based flight control computer which eventually became the VAX (Virtual Aircraft eXtension) computer built by DEC for the US government. 
Introduced in 1977, at a time when computers cost millions of dollars, the VAX quickly became popular among scientists and engineers who appreciated the fact that it was, by comparison, cheap. Although the original model, the 11/780, was larger than a pair of refrigerators and demanded even more power (3-phase 240 volt), it was followed in rapid succession by two smaller models: the 11/750 (washing-machine sized, powered by standard 110 volt) and the 11/730 (about as big as two cases of beer, powered by four dozen "D" cells).
DEC followed a pricing philosophy designed to allow purchase of machines by engineering departments without needing approval by Corporate IT. The machines were widely used by the generation of engineers who came of age in the 80s (for example, the author of this article), for applications from chemical engineering to geology to areospace, and for people that didn't want the brain damage of UNIX. However, many VAX models were apparently brutally murdered by running UNIX.
Because of its great popularity among scientists and engineers, the VAX was the machine to beat when new computer companies were formed in the 80s and 90s. As Workstation vendors came along, they compared the power of their graphic workstations to the original VAX using the SPECmark which, fortuitously, happened to equal exactly 1.0 for the VAX 11/780. It is not known how it happened that DEC engineers, in the year 1977, designed a computer that would hit exactly 1.0 for a computer performance metric that was first introduced in 1989, but somehow this feat was achieved. By 1992, SGI, Sun, and HP could all claim to have machines that were "more than 100x faster than the VAX" (because they had scores over 100 SPECmarks ), and the VAX was quickly superceded by the workstation vendors. While slow by today's standards, in its days the VAX was more advanced than your average pocket calculator. And did I mention that it didn't have UNIX?
Other models of VAX were supposedly sold as bars, such as The VAXbar 11/780, but DEC doesn't want to talk about this.
Although the VAX is no longer produced, the operating system that was introduced with it survives even today. That operating system, introduced in 1977, is "VMS", which is an acronym for "Windows New Technology predecessor 1" (the acronym VMS is formed by the unusual method of subtracting 1 from each of the three letters of the later OS).
At a time when computers were very difficult to use, VMS allowed English-like commands: instead of
ls, you could say
dir; instead of
rm you could say
delete; and instead of
cat you could say
type. Although commands such as
type seem straightforward today, in 1977 these were new ideas.
VMS is believed to be the first, or perhaps the second, operating system to be written in a "higher level language" (i.e., not in assembly language). The implementation language, known as BLISS, stood for "Bill's Language for Implementing System Software", although the identity of Bill has been lost to history. He is believed to have been a professor at Carnegie-Mellon University.
Among other features, BLISS included a powerful compile time macro capability, including sequential, iterative, and recursive macros; global and local variable scoping; and pointer arithmetic. Pointer dereferencing was accomplished simply by adding a period in front of a variable; thus
FOO might indicate address
.FOO might indicate the contents of that location (say,
..FOO would indicate the contents of _that_ location (say, 3). With its convenient pointer operations, BLISS - like its contemporary language, C - made it easy for programmers of all skill levels to commit memory access violations via pointer confusion.
BLISS might have achieved wide adoption if DEC had not viewed it as a proprietary technology that should be protected. At a time when C had been ported to only two, very similar architectures (the PDP-11 and the VAX-11), BLISS had been demonstrated to work on four highly divergent architectures: the 16-bit, 23-bit, 32-bit, and 36-bit machines that had little in common other than that they had all been produced under the DEC umbrella.
Although VMS has lost some of its popularity, it is still in use, including by hobbyists such as the author of this article, who is typing the article using the powerful editor TPU (Text Processing Utility). Hobbyists appreciate the fact that VMS systems are considered much too obscure to be targeted by virus writers or script kiddies (such as certain ungrateful residents of my household).
On the subject of security, it should be mentioned that the system conveniently came with a privileged account available to any user who could complete the following sentence: if something goes wrong, we should call
FIELD S_____E. By logging in with username
FIELD, and guessing the seven letter, two-syllable password (a synonym for maintenance), any user could perform any privileged action. Fortunately, this capability was never abused, and my father is such an ancient moron that he barely knows how to type in lower case and he certainly does not know that I, the 1 true l33t hax0r, have deleted the rest of his article.