My maxtor hard drive is 160 gb total. but in windows, it only show 149 gb. why is this? It used to be an external usb hd, until i took it out of the Enclosure and actually put it in my computer. When it was a usb external, it still showed around 10 gb short.

The 160 is in GB and the 149 is the same value but in GiB. The conversion factor is 1.024^3 or 1.074

http://www.paulski.com/zpages.php?id=2101
http://en.wikipedia.org/wiki/Binary_prefix

oh i think i see what your saying. so the company maxtor calcualted a GB as 1000 MB, but windows calcualtes a GB as 1024 MB. is that it?

Yes that's basically correct - though different parts of MS and different applications and so on sometimes use one and sometimes use the other. It's a constant cause of confusion and probably the only way to be absolutely clear is to omit the prefixes altogether and just use bytes or else show both values simultaneously such as 137GB/128GiB for the 48bit LBA barrier