[1] 16 drive designators (0 through 0FH) are available.Selects the specified drive to be the current, or default, disk drive and returns the total number of logical drives in the system.
Call with:
AH = 0EH
DL = drive code (0 = A, 1 = B, etc.)
Returns:
AL = number of logical drives in system
Notes:
[1] 16 drive designators (0 through 0FH) are available.
[2] 63 drive designators (0 through 3FH) are available.
[3.0+] 26 drive designators (0 through 19H) are available.
To preserve upward compatibility, new applications should limit themselves to the drive letters A—Z (0 = A, 1 = B, etc.).
Logical drives means the total number of block devices: floppy disks, simulated disk drives (RAMdisks), and hard-disk drives. A single physical hard-disk drive is frequently partitioned into two or more logical drives.
[1] [2] In single-drive IBM PC—compatible systems, the value 2 is returned in AL, because PC-DOS supports two logical drives (A: and B:) on the single physical floppy-disk drive. The actual number of physical drives in the system can be determined with ROM BIOS Int 11H.
[3.0+] The value returned in AL is either 5 or the drive code corresponding to the LASTDRIVE entry (if any) in CONFIG.SYS, whichever is greater.
Example:
Make drive B the current (default) disk drive. Save the total number of logical drives in the system in the variable drives.
drives db 0
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mov ah,0eh ; function number
mov dl,1 ; drive 1 = B
int 21h ; transfer to MS-DOS
mov drives,al ; save total drives
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