In checking missions, ADinf automatically identifies file system structure by reading the disk sectors one after another. Three access methods are available for reading the sectors in a drive:

• through direct addressing to BIOS;
• through the use of Interrupt 13h (Int 13h);
• through the use of DOS Interrupt 25h (Int 25h);

For an IDE disk partitioned by the FDISK program, ADinf uses BIOS as the access type.

Access via Int 13h must be used under the following situations. Modern high-capacity disks are manufactured with more than 1024 cylinders (limiting value for standard BIOS of IBM AT). Present-day BIOSes and hard disks support handling of such disks by redusing the number of cylinders and increasing the number of sectors or heads, accordingly (LBA mode). However, if your BIOS does not provide this facility, you may have to use special disk drivers to utilize the full capacity of such disks, for example, Disk Manager for IDE disks. ADinf identifies Disk Manager and automatically defaults to Int 13h as the disk access type. Several drivers exists for SCSI disks. If you have a high capacity SCSI disk in your machine, manually choose Int 13h from the DRIVE ACCESS TYPE box.

Second case. In a machine running under QEMM set to STEALTH mode, ADinf defaults to Int 13h as the DRIVE ACCESS TYPE because access to disk via BIOS is denied to ADinf.

DRIVE ACCESS TYPE must be set to Int 25h for disks managed by special drivers, for example, disk compactors. As a rule, ADinf identifies such situations and automatically defaults to Int 25h. But if the drive name letters in a compacted disk are changed, the drive access type must be set to Int 25h manually by the user.

There are also other situations where the user must specify the drive access type manually, for example, if you have changed the standard sequence of drive specifiers that DOS assigns to disk partitions. DOS allots the drive name letters in the following sequence (if some partition is missing, the letters are shifted accordingly):

First hard disk:
1st Primary DOS  partition C: DIOS
1st Extended DOS partition E: BIOS
2nd Extended DOS partition F: BIOS
3rd Extended DOS partitioh G: BIOS
2nd Primary DOS  partition K: BIOS
3rd Primary DOS  partition L: BIOS

Second hard disk:
1st Primary DOS  partition D: BIOS
1st Extended DOS partition H: BIOS
2nd Extended DOS partition I: BIOS
3rd Extended DOS partitioh J: BIOS
2nd Primary DOS  partition M: BIOS
3rd Primary DOS  partition N: BIOS

ADinf strictly supports this standard sequence of specifiers for assigning names to drives. But, this sequence may be violated in several cases. For the logical drives of name letters up to a violation in the standard sequence, ADinf uses BIOS as the drive access type and Int 25h for the other drives. Below is an example of such a situation. Let us suppose that the second hard disk is an IDE disk with more than 1024 cylinders (without LBA) formatted by Disk Manager. In this case the partitions are allotted drive name letters as follows:

First hard disk:
1st Primary DOS  partition C: BIOS
1st Extended DOS partition D: Int 25h
2nd Extended DOS partition E: Int 25h
3rd Extended DOS partitioh F: Int 25h
2nd Primary DOS partition  G: Int 25h
3rd Primary DOS partition  H: Int 25h

Second hard disk:
Only one Disk Manager partition I: Int 25h

The DRIVE ACCESS TYPE is listed in the right-most column.

One more example of nonconventional configuration. Let us interchange the hard disks in the above example. Let the first hard disk be a large IDE disk partitioned by Disk Manager and the second an ordinary IDE disk. In this case, the drive access type must be set as follows.

First hard disk:
Only one Disk Manager partition C: Int 13h

Second hard disk:
1st Primary DOS  partition D: BIOS
1st Extended DOS partition E: BIOS
2nd Extended DOS partition F: BIOS
3rd Extended DOS partitioh G: BIOS
2nd Primary DOS  partition H: BIOS
3rd Primary DOS  partition I: BIOS