IBM PC DOS is a DOS system for the IBM Personal
Computer and compatibles, manufactured and sold
by IBM from the 1980s to the 2000s.
Released in April of 1987 PC DOS 4.0 added DOS
Shell & support for hard disks drives grater
then 32 MB. PC DOS 4.0 had many bugs and less
free conventional memory than previous PC DOS
3.3. Generally, PC DOS 4.0 regarded as an
unpopular release and was replaced by a never version PC DOS 5.0 in May 1991.