This content is 19 years old. I don't routinely update old blog posts as they are only intended to represent a view at a particular point in time. Please be warned that the information here may be out of date.
A few months back, I was chatting with my Dad about his PC (you know, one of those “family IT support desk” jobs) and he was wondering what had happened to all of his hard disk space. David Chernicoff has written an article for Windows IT Pro magazine about the case of the missing disk space and it’s worth a read. I certainly found it interesting – especially the bit about true sizing cf. disk manufacturers’ idea of storage units.
It’s pretty obvious that if files are deleted and there’s a possibility to restore then, then some disk space should be allocated to keep the deleted files there in compressed format. But cleanup doesn’t actually clean all the files down completely – with the special software, it is still possible to recover deleted files. This is why NASA or some other american agency has a rule that the information is considered non-recoverable only when it’s been overwritten more than 9 times.
@George – I think you mean the NSA (national security – not space exploration) although most government agencies have similar restrictions on securely removing deleted data.
You can use third party tools to securely wipe the free space on the disk – or you can do it with a simple Windows command but, as I recall, this blog post was more about tracking down how you had used up the entire disk than about securely wiping away the remnants of deleted files.