The Fixed Disk Parameter Table, or FDPT, is a structure primarily used by the BIOS in IBM compatible computers, but is also of critical importance to some (especially older) operating systems which do not use the BIOS.
The FDPT was introduced in the IBM PC/XT as a necessity in implementing hard drive (aka fixed disk) support; however, I’ll skip the PC/XT specific details. The IBM PC/AT redefined the FDPT format, but the purpose remained the same: Define the physical characteristics of a hard disk so that the same BIOS ROM could be used with more than a single drive model. Most importantly, the FDPT contained the disk geometry—the number of cylinders, heads, and sectors per track. Continue reading