/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.