> One source says that it's been acceptable to DOS since DOS 2.0 I can confirm that from personal memory. At the time, the biggest vendor of UNIX-like systems

> One source says that it's been acceptable to DOS since DOS 2.0 I can confirm that from personal memory. At the time, the biggest vendor of UNIX-like systems was Microsoft (Xenix), so compatibility was a benefit. They soon sold that product off, though.