Introduction: Geometry Translation

To overcome the geometry limitations imposed by the INT 13h specification, some BIOS drivers translate the IDE drive's actual geometry into a geometry that will fit within the confines of the INT 13h limitations. For Windows 95 to support BIOS level geometry translation, it must be able to determine both the actual and apparent geometry that the BIOS is using. Windows 95 retrieves the apparent geometry from information returned by INT 13h, Function 8. There are three means used to determine actual disk geometry:

• Extract from the Fixed Disk Parameter Table
• Retrieve using the ATA IDENTIFY command
• Retrieve using the Ontrack Disk Manager XBIOS function interface

If all three of these methods fail to produce actual geometry that allows correct access to the drive, the Windows 95 IDE driver unloads and disk access continues to go through the BIOS.