Int 26

INT 26 - DOS 1+ - ABSOLUTE DISK WRITE (except partitions > 32M)
AL = drive number (00h = A:, 01h = B:, etc)
CX = number of sectors to write (not FFFFh)
DX = starting logical sector number (0000h - highest sector on drive)
DS:BX -> data to write

Return:
CF clear if successful
CF set on error
AH = status (see #02547)
AL = error code (same as passed to INT 24 in DI)
AX = 0207h if more than 64K sectors on drive -- use new-style call
may destroy all other registers except segment registers

Notes: Original flags are left on stack, and must be popped by caller. This call bypasses the DOS filesystem, though DOS 5+ invalidates any disk buffers referencing sectors which are written with this call. Examination of CPWIN386.CPL indicates that if this call fails with error 0408h on an old-style (<32M) call, one should retry the call with the high bit of the drive number in AL set. Novell DOS 7 decides whether the old-style or new-style (>32M) version of INT 26 must be used solely on the basis of the partition's size, thus forcing use of the new-style call even for data in the first 32M of the partition. Windows98 will display an error message and deliberately hang the system on attempted write to any hard disk if neither bit 7 of the Extended Drive Info byte nor bit 6 of "DOS_FLAG" (List-of-Lists+60h) is set. Although all registers except segment registers may be destroyed some software depends on some of the registers being preserved. For example some Flash disk drivers requires that DX is not trashed. DR-DOS 7.03 takes care of this.

BUGS: DOS 3.1 through 3.3 set the word at ES:[BP+1Eh] to FFFFh if AL is an invalid drive number. DR DOS 3.41 will return with a jump instead of RETF, leaving the wrong number of bytes on the stack; use the huge-partition version (INT 26/CX=FFFFh) for all partition sizes under DR DOS 3.41. DR DOS 6.0 original releases 05/1991 & 08/1991 reported wrong error codes for "drive not ready" and "write protect". This was fixed

with the DR DOS BDOS patch "PAT321" (1992/02/19, XDIR /C:
947Bh)
and later "full" rebuilds (see INT21/AX=4452h for details).

See Also: INT 13/AH=03h - INT 25 - INT 26/CX=FFFFh - INT

Category: DOS Kernel - Int 26h - @

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