Which MS-DOS?

There is no doubt that MS-DOS, starting with version 5, has finally been augmented to take some notice of the special capabilities of the 386 processor. MS-DOS 4.0 had some facilities that made it able to make use to extended memory and even a simple memory management program to convert extended to expanded memory. however, in MS-DOS 5 these have been improved and extended to include the use of Upper Memory Blocks (UMBs). There is no question that MS-DOS 5 and beyond represents the best choice for a 386 machine.

There are two other versions of MS-DOS that are still in common use with 386/486 systems-MS-DOS 3.3 and MS-DOS 4. MS-DOS 4 has a number of important advantages over 3.3 for 386/486 systems but it gained a poor reputation for reliability when it was first introduced by Microsoft. It contained a number of unfortunate bugs that caused it to loss data stored on disk when its more advanced options were used. This resulted in manufactures and users tending to stay with MS-DOS 3.3 rather than using MS-DOS 4.