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 #01654)
 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
SeeAlso: #01649,#01650,#01652,#01657