Category: DOS kernel
INT 21 - DOS 1+ - SELECT DEFAULT DRIVE AH = 0Eh DL = new default drive (00h = A:, 01h = B:, etc) Return: AL = number of potentially valid drive letters Notes: 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 SeeAlso: AH=19h,AH=3Bh,AH=DBh