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Format of DOS 4.0-6.0 disk buffer

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Offset Size Description

00h

WORD

forward ptr, offset only, to next least recently used buffer

02h

WORD

backward pointer, offset only

04h

BYTE

drive (0=A,1=B, etc) if bit 7 clear
SFT index if bit 7 set
FFh if not in use

05h

BYTE

buffer flags (see #01656)

06h

DWORD

logical sector number (local buffers only)

0Ah

BYTE

number of copies to write
for FAT sectors, same as number of FATs
for data and directory sectors, usually 1

0Bh

WORD

offset in sectors between copies to write for FAT sectors

0Dh

DWORD

pointer to DOS Drive Parameter Block (see #01395 at AH=32h)

11h

WORD

size of data in buffer if remote buffer (see also #01656)

13h

BYTE

reserved (padding)

14h

buffered data

Note:

For DOS 4.x, all buffered sectors which have the same hash value (computed as the sum of high and low words of the logical sector number divided by the number of disk buffer chains) are on the same doubly-linked circular chain; for DOS 5+, only a single circular chain exists.
The links consist of offset addresses only, the segment being the same for all buffers in the chain.

See Also:

#01649,#01650,#01652