When I defrag my 160 GB HD, the useable space for my C drive shows as 143 GB and the D drive shows 5.8 GB useable space. If I remember how to add, this comes to 148.8 GB. Any idea(s) where the remaining 11.2GBs are hiding out ?
"G" is an SI prefix, which means 10^9. In computer applications, G is sometimes but not always defined as 2^30, which lead to such confusion and no real benefit. Modern implementations are starting to use "Gi" to denote the binary version.
http://en.wikipedia.org/wiki/Gigabyte
http://en.wikipedia.org/wiki/Gibibyte
160 GB = 160 * 10^9 B ~ 149 * 2^30 = 149 GiB.
So, assuming a small calculation / overhead factor, everything looks fine, except for the 10^9 vs. 2^30 confusion.
Measurements
should not be this confusing and subject to interpretation according to context. G is an SI prefix, and the problem is due to some computer users using it to mean a different binary amount, which is just confusing and error-prone.