by Gecko » Thu Sep 13, 2007 1:18 am
It's all about Bits vs Bytes and advertising.
All computer data is stored in a binary format as either a one or zero. Eight of these bits together for the most commonly referred to item in computing, the byte. The various amounts of storage capacity are referred by a prefix to represent a specific amount, similar to the metric prefixes.
Since all computers are based on binary math, these prefixes represent base 2 amounts. Each level is an increment of 2 to the 10th power or 1,024.
The common prefixes are as follows:
• Kilobyte (KB) = 1,024 Bytes
• MegaByte (MB) = 1,024 Kilobytes or 1,048,576 Bytes
• Gigabyte (GB) = 1,024 Megabytes or 1,073,741,824 Bytes
• Terabyte (TB) = 1,024 Gigabytes or 1,099,511,627,776 Bytes
Since consumers don't think in base 2 mathematics, manufacturers decided to rate most drive capacities based on the standard base 10 numbers we are all familiar with. Therefore, one Megabyte equals one million bytes while one Gigabyte equals one billion bytes. This isn't too much of a problem with fairly small numbers such as a Kilobyte, but each level of increase in the prefix also increased the total discrepancy of the actual space compared to the advertised space.
Here is a quick reference to show the amount that the actual values differ compared to the advertised for each common referenced value:
• Megabyte Difference = 48,576 Bytes
• Gigabyte Difference = 73,741,824 Bytes
• Terabyte Difference = 99,511,627,776 Bytes
Based on this, for each Gigabyte that a drive manufacturer claims, they are over reporting the amount of disk space by 73,741,824 Bytes or roughly 70.3 MB of disk space. So, if a manufacturer advertises a 320 GB (320 billion bytes) hard drive, the actual disk space is around 297.6 GB of space, roughly 7% less than what they advertise.
And there you have the reason why your 320 gig drive reports as 298 gigs