Offset Size Description 00h WORD forward ptr, offset only, to next least recently used buffer 02h WORD backward ptr, offset only 04h BYTE drive (0=A,1=B, etc), FFh if not in use 05h BYTE flags bit 7: ??? bit 6: buffer dirty??? bit 5: buffer in use??? bit 4: ??? bit 3: sector in data area bit 2: sector in a directory, either root or subdirectory bit 1: sector in FAT bit 0: ??? 06h DWORD logical sector number 0Ah BYTE number of copies to write for FAT sectors, same as number of FATs for data and directory sectors, usually 1 0Bh WORD offset in sectors between copies to write for FAT sectors 0Dh DWORD pointer to DOS Device Control Block (see AH=32h) 11h 3 BYTEs ??? zero or unset garbage 14h buffered data
Note: All buffered sectors which have the same address modulo NDBCH are on the same doubly-linked circular chain. The links consist of offset addresses only, the segment being the same for all buffers in the chain.