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# Why do 2tb hard drives only give you 1.8tb of memory?!

Found 24th Mar 2013
Why do 2tb hard drives only give you 1.8tb of memory?!
Why is the sky blue? Perhaps someone can help us both,
haha what is this, yahoo answer now?!!
Why do people say £2 when the price is £1.96.......
This is 2013 isn't it?
It comes down to Bits and Bytes is the short answer.... the long answer...

All computer data is stored in a binary format as either a one or zero (called a bit). Eight of these bits together are most commonly called a byte. Storage capacity is measured by a prefix to the B (byte) to represent a specific amount, ie K (Kilobyte), M (Megabyte), G (Gigabyte), T (Terabyte) etc. Since all computers are based on the binary system, 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
This is very important information because when a computer operating system or program reports the available space on a drive, it is going to report the overall total of available bytes or reference them by one of the prefixes. So, an OS reporting a total space of 74.51 GB actually has around 80,004,503,306 Bytes of storage space.

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 an 80 GB (80 billion bytes) hard drive, the actual disk space is around 74.5 GB of space, roughly 7% less than what they advertise.
As for why, I don't know. But I DO know it's really annoying. My PS Vita "16GB memory card is around 14GB and my "120GB" hard drive on my PS3 has 111GB