MS-DOS:: /M-S-dos/ [MicroSoft Disk Operating System] n.

:MS-DOS:: /M-S-dos/ [MicroSoft Disk Operating System] n. A
{clone} of {{CP/M}} for the 8088 crufted together in 6 weeks by
hacker Tim Paterson, who is said to have regretted it ever since.
Numerous features, including vaguely UNIX-like but rather broken
support for subdirectories, I/O redirection, and pipelines, were
hacked into 2.0 and subsequent versions; as a result, there are two
or more incompatible versions of many system calls, and MS-DOS
programmers can never agree on basic things like what character to
use as an option switch or whether to be case-sensitive. The
resulting mess is now the highest-unit-volume OS in history. Often
known simply as DOS, which annoys people familiar with other
similarly abbreviated operating systems (the name goes back to the
mid-1960s, when it was attached to IBM's first disk operating
system for the 360). The name further annoys those who know what
the term {operating system} does (or ought to) connote; DOS is
more properly a set of relatively simple interrupt services. Some
people like to pronounce DOS like "dose", as in "I don't work on
dose, man!", or to compare it to a dose of brain-damaging drugs
(a slogan button in wide circulation among hackers exhorts:
"MS-DOS: Just say No!"). See {mess-dos}, {ill-behaved}.
-- The AI Hackers Dictionary