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Format of DOS 4.01 (from UR 25066 Corrctive Services Disk on) disk buffer info:
Offset  Size    Description
 00h    DWORD   pointer to array of disk buffer hash chain heads (see below)
 04h    WORD    number of disk buffer hash chains (referred to as NDBCH below)
 06h    DWORD   pointer to lookahead buffer, zero if not present
 0Ah    WORD    number of lookahead sectors, else zero (the y in BUFFERS=x,y)
 0Ch    BYTE    01h, possibly to distinguish from pre-UR 25066 format
 0Dh    WORD    ??? EMS segment for BUFFERS (only with /XD)
 0Fh    WORD    ??? EMS physical page number of EMS seg above (only with /XD)
 11h    WORD    ??? EMS segment for ??? (only with /XD)
 13h    WORD    ??? EMS physical page number of above (only with /XD)
 15h    BYTE    ??? number of EMS page frames present (only with /XD)
 16h    WORD    segment of one-sector workspace buffer allocated in main memory
                  if BUFFERS/XS or /XD options in effect, possibly to avoid DMA
                  into EMS
 18h    WORD    EMS handle for buffers, zero if not in EMS
 1Ah    WORD    EMS physical page number used for buffers (usually 255)
 1Ch    WORD    ??? appears always to be 0001h
 1Eh    WORD    segment of EMS physical page frame
 20h    WORD    ??? appears always to be zero
 22h    BYTE    00h if /XS, 01h if /XD, FFh if BUFFERS not in EMS