OK. Vaibhav,

Cluster tips are what is left at the end. By "slack space" I was referring to the hidden stuff that gets on an NTFS formatted HDD due to the use of data streams. Probably the wrong term I know, but I am going back to my NT 4.0 days which are somewhat hazy by now

The chkdsk fragments are the "orphaned" bits of files that running chkdsk/scandisk produces. As they are generated as the result of some sort of crash, you never know what sensitive info might be in them?

I just realised that I did not correctly distinguish "free space". This has been marked as "available" but may still contain the previous files' data. Slightly different from the cluster tips that won't get overwritten, as they are not seen as available.

Defragmentation is another issue I forgot to mention. It frequently uses free space on the drive (usually at the end) to reassemble fragmented files before copying them back. Like data streams, you won't be able to see them without forensic tools.