When you wish to retire your old computer, you will do well to delete all files on your hard disk, before giving it away or selling it. However, you should be aware that deletion of files, or even formatting the hard disk, does not remove the data completely from the hard disk. What happens is that the system just removes any reference to the file and the file lies intact on your hard disk, until overwritten by some new file.
This is where Eraser comes in. Eraser is an advanced security tool for Windows which allows you to completely remove sensitive data from your hard drive by overwriting it several times with carefully selected patterns. This leaves no chance for the data to remain on your hard disk and avoids possible misuse. Eraser is a free tool and can be used on Windows XP, Windows 7, 8, 10 and several other platforms, including servers. So before you chuck out your old machine, remember to delete ALL your data effectively.