Forget bits and binary... They aren't really related to the problem here...

In English, "kilo" means thousand, "mega" means million, giga means billion,
"tera" means trillion, etc...

A "five kilogram" bag of sugar weights 5,000 grams. "25 megawatts" of power
is 25,000,000 watts. To a person, a megabyte is a million bytes. A gigabyte
is a billion bytes.

The reason for this is that 1,000 is a natural boundary for people to use.
Would it make any sense that a kilo is 893 of something? No, because we can
count to 999 before we need to add more digits.


In computer terminology, "kilo" means 1,024, "mega" means
1024x1024=1,048,576, "giga" means 1024x1024x1024=1,073,741,824, "tera" means
1024x1024x1024x1024=1,099,511,627,776.

The reason that computer terminology bases it's numbering system around
1,024 is because it's a natural boundary for computers. Since computers use
base 2, their boundaries are numbers like 8, 16, 32...etc...1024,
2048...etc...1073741824, 2147483648, 4294967296...etc. Writing these in base
2 we can see the pattern... 1000 is 8, 10000 is 16, 100000 is 32, 1000000000
is 1024, 10000000000 is 2048, 10000000000000000000 is 1073741824,
100000000000000000000 is 2147483648.

So when you buy your drive at the store, the saleman tells you it has
100gigabytes, meaning it has 100 billion bytes of space. When you put it in
your computer, it will tell you that you have a 93gigabyte drive, meaning
that you have 93x1024x1024x1024 bytes of space (93.1322... actually).

Now, on top of this, the drive must be formatted before it can be used at
all, so some space will always be used by your file system, even on an empty
drive, to keep track of empty drive space, partitions, etc. Also, the
manufacturer uses some of the drive to map sectors, etc. Any empty drive
really isn't empty at all.