Often, diagnostics programs use the INT13h interface to talk more directly to the drive, bypassing
the operating system and working directly with the BIOS. An example of this type of program
would be hard disk low-level format programs or the DiskEdit program that comes with the
Norton Utilities, and which allows direct editing of disk sectors, file allocation tables, directories,
etc. This type of access is accomplished by sending INT13h commmands directly instead of working
with the higher level INT21h operating system commands. INT21h commands are fileoriented,
while INT13h commands are cylinder, head, and sector oriented.
Anytime a program uses INT13h commands, an error status is returned after each command. If
an error occurs, the status will be reported as a number other than 00h, and most programs will
then attempt to display this error to the user. Table 21 shows the error codes that might be
returned by the BIOS INT13h routines. In some cases you may see these codes referred to when
running a low-level format program, disk editor, or other program that can directly access a disk
drive through the BIOS.