Format of DOS 4.x disk buffer hash chain head (array, one entry per chain)

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Offset	Size	Description
00h	WORD	EMS logical page number in which chain is resident, -1 if not in EMS
02h	DWORD	pointer to least recently used buffer header. All buffers on this chain are in the same segment.
06h	BYTE	number of dirty buffers on this chain
07h	BYTE	reserved (00h)

Note:

Buffered disk sectors are assigned to chain N where N is the sector's address modulo NDBCH, 0 <= N <= NDBCH-1.
Each chain resides completely within one EMS page.
This structure is in main memory even if buffers are in EMS.