DOS Plus (erroneously also known as DOS+) was the first operating system developed by Digital Research's OEM Support Group[1] in Newbury, Berkshire, UK, first released in 1985.

There is an AUTOEXEC.BAT file, but no CONFIG.SYS (except for FIDDLOAD, an extension to load some field-installable device drivers (FIDD) in some versions of DOS Plus 2.1).

This so-called floating drive feature allows old programs which don't support subdirectories to work under DOS Plus and can be used to make file handling at the command prompt much easier.

(For similar reasons, the appendage to the environment block associated with loaded applications under MS-DOS/PC DOS 3.0 (and higher) contains a reference to the load path of the executable, however, this consumes more resident memory, and to take advantage of it, support for it must be coded into the executable, whereas DRI's solutions transparently works with any kind of application.)

These features can be attributed to the fact that CP/M itself did not have a concept of subdirectories, and DOS was emulated under these operating systems, so directories had to be translated to internal CP/M structures in some intelligent way.

This file is in the CP/M-86 CMD format, and is structured internally as a number of modules: DOS Plus was the main operating system in ROM for the Philips :YES, for which it was originally developed.

[1][nb 1] PC compatible versions were supplied with the Amstrad PC1512[1] and the Jasmin Turbo from the French company T.R.A.N. S.A.