Function 440Dh Minor Code 61h Read Track on Logical Drive

mov bx, Drive ;0 = default, 1 = A, 2 = B, etc.

mov ch, 08h ;device category (must be 08h)

mov cl, 61h ;Read Track on Logical Drive

mov dx, seg ReadBlock

mov ds, dx

mov dx, offset ReadBlock ;ds:dx points to RWBLOCK structure

mov ax, 440Dh ;IOCTL for Block Device

int 21h

jc error_handler ;carry set means error

Read Track on Logical Drive (Function 440Dh Minor Code 61h) reads data from a track on the specified device and places the data in memory.

Parameters

Drive

Specifies the drive to be read from (0 = default drive, 1 = A, 2 = B, etc.).

ReadBlock

Points to an RWBLOCK structure that contains information that specifies the sectors to be read from. The RWBLOCK structure has the following form:

RWBLOCK STRUC

rwSpecFunc db 0 ;special functions (must be zero)

rwHead dw ? ;head to read/write

rwCylinder dw ? ;cylinder to read/write

rwFirstSector dw ? ;first sector to read/write

rwSectors dw ? ;number of sectors to read/write

rwBuffer dd ? ;address of buffer for read/write data

RWBLOCK ENDS

For a full description of the RWBLOCK structure, see Chapter 3, “File System.”

Return Value

If the function is successful, the carry flag is clear. Otherwise, the carry flag is set and the AX register contains an error value, which may be one of the following:

Comment

Read Track on Logical Drive returns 0002h (ERROR_FILE_NOT_FOUND) if the specified drive number is invalid.

See Also

Function 440Dh Minor Code 41h Write Track on Logical Drive