How does drive capacity is calculated?

Different applications like FDISK, CHKDSK, Windows, BIOS, etc., use different methods and numbering systems to calculate hard drive capacities. The two most common numeric representations of the hard drive capacity are presented in the base 10 (decimal) and base 2 (binary) numbering systems. The basic formula to calculate the capacity of a drive is: Cylinders * Heads * Sectors * 512 (bytes per sector)

This formula calculates a number representing the total number of bytes (characters) that can be stored on the hard drive. This is a decimal number, to convert this number to the decimal equivalent of the binary Megabytes (MB) or Gigabytes (GB), this value must be divided by the decimal value of a binary MB or GB. The decimal equivalent of 1 MB (220) is 1,048,576 and 1 GB (230) is 1,073,741,824.

Here is an example for a 3.5 GB hard drive:
6,800 * 16 * 63 * 512 = 3,509,452,800 bytes or 3.5 GB using 106 or decimal values
The equivalent in binary MB is 3,509,452,800 / 1,048,576 = 3,346 MB
The equivalent in binary GB is 3,509,452,800 / 1,073,741,824 = 3.268 GB

You will find the capacities of all Maxtor IDE, EIDE & Ultra DMA drives in both binary and decimal values in our IDE_CMOS Table.

Close this Window