Int 21H, AH=0EH

1 and higher

SELECT DEFAULT DRIVE

DosSelectDisk

• AH = 0Eh
• DL = new default drive (00h = A:, 01h = B:, etc)

• AL = number of potentially valid drive letters

under Novell NetWare, the return value is always 32, the number of drives that NetWare supports

under DOS 3.0+, the return value is the greatest of 5, the value of LASTDRIVE= in CONFIG.SYS, and the number of drives actually present on a DOS 1.x/2.x single-floppy system, AL returns 2 since the floppy may be accessed as either A: or B: otherwise, the return value is the highest drive actually present

DOS 1.x supports a maximum of 16 drives, 2.x a maximum of 63 drives, and 3+ a maximum of 26 drives

under Novell DOS 7, this function returns the correct LASTDRIVE value even when the undocumented LASTDRIVE=27..32 directive was used in CONFIG.SYS

“parse FCB” (see AH=29H) can be used to determine whether a drive letter is valid

AH=19H,AH=3BH

Text based on Ralf Brown Interrupt List Release 61