Int 25h Absolute Disk Read Superseded
Reads from one or more logical sectors on the specified drive and
copies the data to the specified buffer.
Note Int 25h has been superseded. Programs should use
Read Track on Logical Device (Int 21h, function
440Dh, minor code 61h).
Drive < 32 MB Drive >= 32 MB (DOS 3.31+)
Entry AL = Drive number Drive number
DS:BX = Addr of data buffer Addr of DiskIO structure
CX = No. of sectors to read 0FFFFh
DX = First sector to read Ignored if CX = 0FFFFh
Return Note The flags register is left on the stack
Expect BP to be changed
If CF is clear, disk sectors read into buffer
or
If CF is set, AL and AH contain error values
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The drive number in AL must be set to 0 for drive A:, 1 for drive
B:, 2 for drive C:, etc. If the size of the specified drive is
greater than or equal to 32 MB (CX = 0FFFFh), the DiskIO structure
is required (DOS 3.31+).
On return, Int 25h leaves the CPU flags on the stack. Programs
should check the carry flag for an error before popping the flags
from the stack.
Int 25h does not process critical errors. If one occurs, the
interrupt routine returns an error value to the program but does
not issue Int 24h.
Int 25h reads logical sectors only. This means, for example, that
it cannot read hidden sectors.
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If Int 25h returns the carry flag set, AL and AH contain error
values. The AL register specifies device-driver errors and
contains one of the following values:
Value Meaning
01h Unknown unit
02h Drive not ready
04h CRC error in data
06h Seek error
07h Unknown media type
08h Sector not found
0Bh Read fault
0Ch General failure
0Fh Invalid media change
For most computers, the AH register specifies ROM BIOS errors and
may contain one of the following values:
Value Meaning
01h Bad command
02h Address mark not found
04h Sector not found
10h Data error (CRC error)
20h Controller failure
40h Seek failure
80h No response from drive