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Format of DOS 5.0-6.0 disk buffer info

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Offset Size Description

00h

DWORD

pointer to least-recently-used buffer header (may be in HMA) (see #01655)

04h

WORD

number of dirty disk buffers

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

buffer location
00h = base memory, no workspace buffer
01h = HMA, workspace buffer in base memory

0Dh

DWORD

pointer to one-segment workspace buffer in base memory

11h

3 BYTEs

unused

14h

WORD

???

16h

BYTE

flag: INT 24 fail while making an I/O status call

17h

BYTE

temp storage for user memory allocation strategy during EXEC

18h

BYTE

counter: number of INT 21 calls for which A20 is off

19h

BYTE

bit flags
bit 0 : ???
bit 1 : SWITCHES=/W specified in CONFIG.SYS (don't load WINA20.SYS when MS Windows 3.0 starts)
bit 2 : in EXEC state (INT 21/AX=4B05h)

1Ah

WORD

offset of unpack code start (used only during INT 21/AX=4B05h)

1Ch

BYTE

bit 0 set iff UMB MCB chain linked to normal MCB chain

1Dh

WORD

minimum paragraphs of memory required by program being EXECed

1Fh

WORD

segment of first MCB in upper memory blocks or FFFFh if DOS memory chain in base 640K only (first UMB MCB usually at 9FFFh, locking out video memory with a DOS-owned memory block)
the MCB this word points at contains a valid link into high memory even if it is marked with a 'Z' indicating the last memory block

21h

WORD

paragraph from which to start scanning during memory allocation

See Also:

#01652,#01653