'Long Function to determine amount of free space on a drive
'Parameter to function is the drive specifier.
'0 = default drive, 1 = A:, 2 = B:, etc.
'Returns # of bytes free as a double-precision #
'Returns -1 if drive specifier is invalid
:
LONG FN GetSpace#(DRIVE)
MACHLG &B4, &36           : ' MOV AH,36H
MACHLG &8A, &16, DRIVE    : ' MOV DL,[DRIVE]
MACHLG &CD, &21           : ' INT 21H
MACHLG &3D, &FFFF         : ' CMP AX,FFFFH
MACHLG &75, &06           : ' JNE +6
MACHLG &BB, &01, &00      : ' MOV BX,1
MACHLG &B9, &01, &00      : ' MOV CX,1
MACHLG &A3, AX            : ' MOV [AX],AX
MACHLG &89, &1E, BX       : ' MOV [BX],BX
MACHLG &89, &0E, CX       : ' MOV [CX],CX
Free# = AX * BX * CX * 1.0
END FN = Free#
: