Format of DOS 4.01 (from UR 25066 on) disk buffer info:

Offset  Size    Description
 00h    DWORD   pointer to array of chain heads (see below)
 04h    WORD    number of disk buffer chains (referred to as NDBCH below)
 06h    DWORD   pointer to lookahead buffer, zero if not present
 0Ah    BYTE    number of lookahead sectors, else zero (the y in BUFFERS=x,y)
 0Bh  9 BYTEs   ???
 14h    DWORD   pointer to workspace buffer, purpose ???, allocated in main
                memory if BUFFERS/XS or /XD options in effect
 18h    WORD    EMS handle for buffers, zero if not in EMS
 1Ah    WORD    EMS physical page number used for buffers (usually 255)
 1Ch    WORD    ??? seems always to be 1
 1Eh    WORD    segment of EMS physical page frame
 20h    WORD    ??? seems always to be zero