Why is there a discrepancy between the size of my hard disk and the size reported by Windows and DiskView?
"I have a 120 GB hard drive but Windows XP claims it's size is 111.8 GB. What has happened to the other 8.2 GB? "
Hard drive manufacturers calculate hard disk size in 'base 10' notation while Windows does the calculation in 'base 2' (binary) format. Both the manufacturer and Windows are giving you the "correct" number.
1 Gigabyte as defined by a manufacturer is 1,000,000,000,000 Bytes. This makes sense in the metric base 10 sense as we define kilo as 1000, mega as 1,000,000 and giga as 1,000,000,000,000.
Windows, however, calculates the disk size in a base 2 system. Base 2 does not convert into base 10 exactly in most cases but back in the day it was close enough so that a kilobyte was defined as 2^10 or 1024.
2^10 is 1024 is 1 kilobyte
2^20 is 1048576 or 1 megabyte
2^30 is 1073741824 or 1 gigabyte
When the hard disk manufacturer sold you a 120 Gig hard drive, they were selling you 120,000,000,000 bytes. Windows divides this number by what it considers a GB (1073741824) and reports the hard disk size as:
120000000000 (bytes) / 1073741824 (bytes per GB) = 111.8 GB
This accounts for the 'missing' 8.2 GB in the hard disk's size. You still have 120,000,000,000 bytes to use but because of inconsistent definitions of what kilo, mega and giga really represent, there is an inconsistency in the measurement of size.
Read other frequently asked questions in the DiskView FAQ.
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