In answer to your first question, no there is no single button that will do it all for you. You need to know what you want erased so that you don't erase things you (or Windows) need.
The time it takes to erase depends on a few different factors, such as the amount of data that needs to be overwritten, the speed of your CPU, the amount of RAM (memory) your system has, how many times you are overwriting the space, and any other programs running at the same time. With 64 gigs, 3-6 hours for a single pass is not unusual, depending on the system.
I'm currently running an unused disk space sweep and it's still going after 9 hours. I'm using the Gutmann method with 35 passes. So presumeably it could take days to complete, with 64gigs to scan? Or has something gone wrong?
Am I correct in thinking, the unused disk space scan, will NOT harm any existing files and it is only interested in blank areas, possibly containing deleted files from the past?
Well, TriggerTV, I feel bound to respectfully ask why you feel the need to accomplish the 35 passes of the Gutmann method! I f you do not work for the CIA,or don`t have GMs ten year business plan on your machine,I feel there is a little overkill here!
To put it another way,if 35 passes are really necessary,maybe you should not be putting such info on your hard drive. For most users,a few passes will ensure enough privacy,and Eraser used correctly is superb for the job. Do please read the help file most thoroughly tho.
A neat free application for examining the effectiveness of a disc wiping program is at: http://www.theabsolute.net/sware/dskinv.html