I actually just went thru this a few minutes ago. My son gave me a 500G drive he didn't need anymore so I put it in an external enclosure, plugged it in to my computer and did a quick format. The drive showed as 160G. WTH? Went into Disk Management where I could see there were some non-windows partitions. I deleted those then extended the NTFS partition. Now I have the whole 500G. If I was really determined and my son's data had some value I might be able to recover that data but for my purposes, the drive is as clean as I need it to be.