Hard drive capacity is defined in terms of decimal (base 10) capacity. In decimal notation, one megabyte (MB) is equal to one million bytes and one gigabyte (GB) is equal to one billion bytes. We are most accustomed to the decimal system in everyday life. However, computers use the binary (base 2) numbering system. In the binary numbering system, one megabyte is equal to 1,048,576 bytes, and one gigabyte is equal to 1,073,741,824 bytes.

Both Windows and Mac OS use the binary numbering system. When you use your system to check your drive’ capacity, multiply the value shown (displayed in base 2 megabytes) by 1,048,576 to determine the decimal equivalent for the hard drive’s capacity.

Here is an example of a 160 GB drive running on a windows system (all versions):

? Double-click on the My Computer icon.
? Choose the eternal hard drive
? Right-click on the external hard drive and select Properties.

An information box will appear displaying the drive’s capacity in both the numbering systems showing 152 GB and 163,921,571,840 bytes (assuming the model is labeled 160 GB).