Function 440Fh Set Logical Drive Map

mov bl, Drive ;0 = default, 1 = A, 2 = B, etc.

mov ax, 440Fh ;Set Logical Drive Map

int 21h

jc error_handler ;carry set means error

Set Logical Drive Map (Function 440Fh) sets the active drive number for a physical drive that has more than one logical drive number.

Parameter

Drive

Specifies the drive number to set (0 = default drive, 1 = A, 2 = B, etc.).

Return Value

If the function is successful, the carry flag is clear, and the AL register contains the active drive number for the corresponding physical drive. If the physical drive has only one drive number, the AL register contains 00h.

If the function is not successful, the carry flag is set and the AX register contains an error value, which may be one of the following:

Value

Meaning

0001h	ERROR_INVALID_FUNCTION
0005h	ERROR_ACCESS_DENIED
000Fh	ERROR_INVALID_DRIVE

Comments

Programs that set the active drive prevent MS-DOS from prompting the user with the message “Insert diskette for drive x: and press any key when ready.”