After looking at my own hard drive; Program Files (x86) uses up about 45GB, Windows uses about 5GB, and System Restore uses up 12% every time it creates a restore point (whether it be after installing an update, (un)installing a program, and the daily restore points)...so after 5 years of never deleting a single restore point, guess where all the used space is. It's in System Restore.
To delete these points, go to:
Start--Control Panel--System and Maintenance--Administrative Tools--Free up disc space--Disc Cleanup--More Options--System Restore and Shadow Copies " Clean up "
Cleaning up System Restore will take a few minutes, but you'll be able to retrieve a great deal of space (after only a couple of weeks, I can usually retrieve about 15 to 20GB of space)
My grandson brought me the hard drive from his dead computer so I could get his files & folders off of it using my USB adapter. It's 250GB. The main partition is 229GB. It shows that 170GB as used, with 59GB free space.
The strange thing is, the total size of all the folders within the drive adds up to only 93GB. So 77GB is unaccounted for. That's a lot. Before transfering anything, I scanned the drive with Malwarebytes, Super-Antispyware, and AVG A/V and found 8 or 9 infections, mostly trojans. I also did a defrag, which made no difference in used space. Also, IF his system restore was set at the max of 12%,that could be 30GB (where is that stored?). Either way, there is a lot of unaccounted-for used space. Could it all be a result of trojans and other malware building up for 5 years?