Hard Drive Size
Here’s the scenario. You just bought a new 750 GB hard drive. You open your computer case, install your new hard drive and turn on your computer. When your system finishes loading, you look at your 750 GB hard drive and find that your computer only sees 699 GB. What’s that about?
Don’t worry, you are not actually missing 50 GB. Many people seem a little confused to where the 50 gigabytes go. Some people think that it has to do with formatting the hard drive, or that there is some special area that the hard drive is not suppose to use. While this may be partly true, the answer is actually right on the box or paper insert of most retail hard drives. The label says something like, “One gigabyte, or GB, equals one billion bytes when referring to hard drive capacity. One terabyte, or TB, equals 1,000 gigabytes when referring to hard drive capacity. Accessible capacity may vary depending on operating environment and formatting.”
Taken from Wikipedia,
Most operating-system tools report capacity using the same abbreviations but actually use binary prefixes. For instance, the prefix mega-, which normally means 106 (1,000,000), in the context of data storage can mean 220 (1,048,576), which is nearly 5% more. Similar usage has been applied to prefixes of greater magnitude. This results in a discrepancy between the disk manufacturer’s stated capacity and the apparent capacity of the drive when examined through most operating-system tools. The difference becomes even more noticeable for a gigabyte (7%), and again for a terabyte (9%). For a petabyte there is a 11% difference between the SI (1000^5) and binary (1024^5) definitions. For example, Microsoft Windows reports disk capacity both in decimal-based units to 12 or more significant digits and with binary-based units to three significant digits. Thus a disk specified by a disk manufacturer as a 30 GB disk might have its capacity reported by Windows 2000 both as “30,065,098,568 bytes” and “28.0 GB”. The disk manufacturer used the SI definition of “giga”, 109 to arrive at 30 GB; however, because Microsoft Windows, Mac OS and some Linux distributions use “gigabyte” for 1,073,741,824 bytes (230 bytes), the operating system reports capacity of the disk drive as (only) 28.0 GB.
What this means is that the drive manufacturers are using the standard definition of the prefixes kilo, mega, giga, etc (multiples of 10), whereas the operating systems use the same prefixes, but are calculating based on powers of 2. Operating systems define a kilobyte as 1024 bytes, a megabyte as 1024 kilobytes (or 1,048,576 bytes), a gigabyte as 1024 megabytes (or 1,073,741,824 bytes) and so on. SO, here is what is happening to the 750 GB hard drive in the example above:
750 GB = 750,000,000,000 bytes according to the manufacturer. To the manufacturer, and the international standard definition for prefixes, a gigabyte is 10^9 bytes. Since the drive actually contains 750,000,000,000 bytes, the operating system takes the total bytes and divides by 2^30, which is the binary definition of giga. 750,000,000,000 divided by 2^30 is 699 GB. Another way to look at this is the operating system could report the drive as 732,421,875 KB (750,000,000,000 divided by 1024) or 715,256 MB (750,000,000,000 divided by 1024 twice).
As far as the formatting or special no-use area of the hard drive, formatting methods (FAT, NTFS, EXT3, HFS+) does have some small effect on the final drive capacity. There are also some no-use areas of the hard drive that are only used in certain circumstances, but that is a subject for another article.
So your 50 GB isn’t missing, it’s still there. Your hard drive capacity is just being reported using different units.