DL drive number (0=A, 1=B, etc.) to become the default disk
Returns: AL total number of system drives
Info: The drive identified in DL becomes the current DOS default drive
(if it is a valid drive number).
Error test; use DOS Fn 19H (Get CurDisk) to make sure it worked.
Notes: The return value in AL is number of drives of any type,
including hard disks and 'logical' and phantom drives (such as
drive B: in a 1-floppy system).
The return value is simply a count of valid drive IDs--not an
indication of which drive IDs are valid.
This call triggers a critical error (INT 24H) when you select a
drive that does not contain a diskette.
Versions: DOS 3.0+ AL is the same as the value of LASTDRIVE=, as specified
in CONFIG.SYS. The a typical default LASTDRIVE is 5.
See Also: 3bH (set default directory