The description below is from the book DOS the
Easy Way by Everett Murdock Ph.D.
for information about downloading the book.
Type: Internal (3.0 and later)
Purpose: Used in the CONFIG.SYS file to set the maximum number of
that can be accessed.
If you set the available disk drives to a letter value lower than that
by your existing system, DOS will automatically override the letter value
accommodate the drives installed in your system. You should only
number of drives if you are actually going to be using additional drives
each drive letter above E decreases the amount of RAM available for other
You do not need to use LASTDRIVE to assign a drive letter to devices that
are loaded in your CONFIG.SYS file.
For more information about the LASTDRIVE command, see Chapter 6, Tips for Advanced Users, in the downloadable book DOS the Easy Way.
drive letter - Specifies the last disk drive (A to Z) that will be
available. The default is E or the last drive specification in use on your system.
To increase the number of drives that can be accessed by DOS to 4, enter