You cannot use the full size of a hard disk but it shouldn't be to the extent that you are mentioning. This is due to cluster sizes and the fact that manufacturers quote disks as megabits rather than megabytes (hope I didn't lose you there). for example, I have a 163GB hard drive, once formated it only has 152GB available, it has lost 11GB. This is emphsised more in the bigger hard drives. Yours will lose some but not that much.
My invisible partition for restore was 4GB, this is set by the vendor, not Windows itself.
Try running error checking or scandisk for that drive in windows, it will tell you if there are any errors and give you a report.
What version of Windows do you have?
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