The description below is from the book DOS the
Easy Way by Everett Murdock Ph.D.
for information about downloading the book.
Type: External (3.1 and later)
SUBST d: d:path
SUBST d: /D
Purpose: Substitutes a virtual drive letter for a path
Use the SUBST command to substitute a drive letter for a path in order to
a virtual drive (a reserved area rather than an actual disk drive) as a
In order to enter drive designations using any letter (other than just
letters for the physical drives installed in your computer), you may have
this line to a CONFIG.SYS file that should be placed in the root
your startup drive:
Six DOS commands cannot be used with virtual drives created with the
SUBST command. They are:
If you enter the SUBST command without options , the program will display
name of the current virtual drives that are in effect (if any).
For more information on SUBST and other hard disk commands, see Chapter 3,
Using Fixed Disks, in the downloadable
book DOS the Easy Way.
To create a virtual drive F for the path, SALES\LETTERS (under the root
directory) of drive C, enter
subst f: c:\sales\letters
Read and write requests to either drive F or to C:\SALES\LETTERS will be
stored in the C:\SALES\LETTERS directory area.