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). 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!").