Microsoft MS-DOS 4.0 was version 4.0 of the Microsoft Disk Operating System (MS-DOS).
MS-DOS 4.01 introduced the MS-DOS Shell. The Dos Shell was a Graphical program that made using MS-DOS a little easier. Extended memory support was also included as was support for hard disk partitions upto 2 gigabytes. The SmartDrive Disk Caching utility was also included