Many of the Microsoft windows users complain their storage devices like hard disks and flash drives show a less capacity in windows operating systems than manufacturer mentioned capacity. For example 4 GB pen drive usually have a capacity of about 3.72 GB. 320 GB hard disk has about a capacity of about 300 GB. People give different opinions as reason for this. Some says windows allocate some space for back up process. Some accuse the manufacturer. But actually the mentioned capacity is there. Reason is a matter of using different unite.