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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.