INT 21,69 - Get/Set Disk Serial Number (Undocumented DOS 4+)

AH = 69h

AL = 00 get serial number

= 01 set serial number

BL = drive (0 = default, 1=A:, 2 = B:, ... )

DS:DX = buffer to contain extended BIOS Parameter Block (~BPB~, AL=0)

= disk information to set of the form:

% Offset Size Description

00 word info level (zero)

02 dword disk serial number (binary)

06 11bytes volume label or "NO NAME " if not present

11 8bytes filesystem type string "FAT12 " or "FAT16 "

returns:

CF = set on error

AX = error code if CF set

= 01 network drive not supported

= 05 no extended BPB found on disk

CF = clear if successful and value in AX is destroyed

AL = 00 buffer filled from Extended BPB on disk

= 01 disk Extended BPB updated from buffer

DS:DX = pointer to returned data, when AL = 0

- copies data from Extended BIOS Parameter Block to buffer

- no critical error is generated on error

- does not work on network drives (returns 01)

- returned buffer (after offset 2) is similar to offsets 27 through

3D of the Extended BPB found in the boot record

- see ~INT 21,59~