The issue with recovering "memory" (actually storage space) with hard drives is the way that information is stored. Files are stored in the first available space the computer finds on the drive. So if you have a 1MB Word file..it finds the first space available. If the first space available is only 500KB, then it will put part of the file there and the other half elsewhere... when the hard drive is brand new...generally files stay in one piece... but as you go about deleting things, you have holes.... and when you save new things.. if splits your file to fill the holes. Your computer keeps track of all the pieces with an Index at the beginning of the drive. (corrupt the index, you are SOL). (I am trying to avoid technogeek as much as possible).
It would be like going to the library and having no real order in the shelving. The library got cheap and hired fools to reshelve books and they just walk down the shelf stack until they find a hole and put the book there...and the manager, rather than putting it where it belongs, just makes a note and puts the note in a book of notes (index)... and if you want to find that book..you have to look in that notebook to find what you want... worse...if the hole for the book isnt large enough..the idiot rips the book in half and puts one part there and the other part in another hole. thats what the hard drive is doing...
The other issue is that depending on how big your hard drive is and how (or if) it is partitioned. Data is dropped into little sections. If your file does not take up the whole section, it doesnt matter. The whole section is "FULL" even if it is only partially filled with the file. This is where the waste of space comes in.
The key to gaining space back is to partition larger hard drives to make better use of the smaller sections. Also making sure that you defragment your hard drive periodically. Defragmenting the hard drive takes all of the scattered pieces of files and places them together, storing them efficiently...it also speeds up the process of finding a file or running a program. People who burn lots of CDs, videos, etc tend to have this issue more than those who just save documents from time to time. in the library illustration, eventually it would become to cumbersome and someone has to go in and clean that mess up...thats what defragmenting does.
(By the way, grocery stores do the exact same thing. Ever go to the store and see things have been moved around when you were used to a different way? Yep...the grocery store defragmented its shelves..another story for another time.)
Here is a link to useful ways to reclaim lost hard drive space: http://www.pcworld.com/printable/article/id,97442/printable.html
Whatever you do..back up your files (to an external hard drive, online storage, or a USB flash drive) before messin around with the hard drive.
Snakes ()