Drives 8.4 GB and larger all use the same parameters: 16383 cylinders, 16 heads, and 63 sectors. This is due to a limitation designed into the original IDE interface. Hard drives identify themselves to the system BIOS using the "Identify Drive Data." The original design of the IDE interface allowed for values up to 16383 x 16 x 63 (around 8.4 GB) to be used in the Identify Drive Data. In order for drives to identify themselves as being larger than 8.4 GB, a new method was needed. This new method was added on to the Identify Drive Data, and is known as the "Extended Functions."
The extended functions communicate drive size in a more straightforward manner, simply telling the BIOS how many sectors are available on the drive (the capacity can then be calculated by multiplying the number of sectors times 512 bytes). Once the Extended Functions are used, the Cylinders, Heads, and Sectors on the drive are no longer important. All hard drive manufacturers agreed that drives larger than 8.4 GB would report the maximum number of cylinders, heads and sectors, which is 16383 x 16 x 63. The actual size of the drive must be determined by the Extended Functions. Some manufacturers may list larger parameters with their drives, but these drives will still only be able to report 16383 x 16 x 63 in the Identify Drive Data.
In order to make use of drives larger than 8.4 GB, both the system BIOS and the Operating System must be able to interpret Extended Functions. Older Operating Systems such as DOS 6.22 and Windows 3.1 are not able to interpret Extended Functions, so they will never be able to use drives larger than 8.4 GB even with the use of Data Lifeguard Tools. Newer OS's, such as Windows 95, 98, and NT are capable of handling larger drives. Windows 95 and 98 require that the system BIOS also support the Extended Functions, while NT only requires that Service Pack 3 be installed. Other OS's such as OS/2 may require special patches to access drives larger than 8.4 GB. Consult your software manufacturer for specifics.
//Regards Soaplover