If you look at your Windows computer’s hard drive, you will notice that you have less space than the advertised size.  While you may have a 1TB hard drive, Windows shows less than 1TB of storage. Though some of the reason are invisible shadow files, formatting overhead, hidden recovery partitions, boot sectors; there is one main reason you have less than advertised hard drive space.

Why Do I Have Less Space Than Advertised In Windows?

To know the reason there is a difference in space between hard drive manufacturers, you have to refer to math about exponents. While hard drives uses a base 10 notation for calculating hard drive space, Windows calculates it using a base 2 notation. Hard drive calculates every new prefix in increments of 1000, while Windows calculate any new prefix in increments of 1024.

To hard drive manufactures, every 1000 is a new prefix. 1000 byte is a kilobyte; 1000 kilobyte is a megabyte; 1000 megabyte is a gigabyte; and 1000 gigabyte is a terabyte.

To Windows, every 1024 is a new prefix. 1024 byte is a kilobyte; 1024 kilobyte is a megabyte; 1024 megabyte is a gigabyte; and 1024 gigabyte is a terabyte.

So technically, they are both correct in calculating hard drive space; even though they have different results.

Who Else Does This?

Before Mac OS X Snow Leopard, Apple’s Mac OS calculates space similarly to Microsoft’s Windows (using a base 2 notation). When Mac users upgraded to Mac OS X Snow Leopard, they reported more space. The reason for the more reported space is how Apple calculates space; switching from base 2 to base 10 notations.