My new 80 GB hard disk shows 74.5 GB on the computer!!

One constant source of confusion for buyers of hard disk is the disparity between advertised size of the hard disk and the capacity that is reporte by the Operating System.More than one buyer has felt confused when they installed their shiny new 80 GB hard disk ,for instance only to find that the operating system tels them that the disk only has a 74.5 GB capacity .This is not actually an error ,but an holdover of the different ways in which the hard drive vendors and the software systems measure capacity .When calculating their disk size , hard drive vendors use the decimal definition of Gigabyte.That is one GigaByte equals 1000 MegaBytes .One MegaByte equals 1000 KiloBytes and so on.
The Operating System however will use the binary definition of a Gigabyte when calculating available space that is 1 GigaByte equals 1024 MegaBytes .
So using a decimal definition , a hard disk with 80,000,000,000 bytes of storage is 80 GB.But in binary terms that’s a little less than 75 GB.
Thats the reason why the hard disk space shown by the Operating System comes out to be less than the Advertised Hard disk space.