Simple Questions Arising From File Deletion Issues

I came across a thread in the MG hardware forum about erasing a hard disk. Not wanting to hijack or resurrect that thread has led me to this, to question some things

I've been looking on the internet, and this has told me that

A Quick Format erases only the File Allocation Table of a disk (which is what I had always believed), but left the actual data intact.

A Full Format does what, precisely ? I have read that it is simply a Quick Format with a chkdsk , but I suspect that it is actually more than this. The Microsoft article I found on this was with reference only to installing operating systems. Can anyone direct me to a good, reliable article on this ?

In the MG article I was reading, it was apparent that CCleaner (which I have) had a good routine for permanently erasing all disk files so that reading them was impossible. For individual files I have come across a program called Sdelete by Sysinternals (Microsoft). Both of these offer the facility for "multiple passes". If you have a program that writes 0s to every location so that when read you get 0s back every time, why is there any need for "multiple passes" :confused

With reference to this post, I am Windows XP Home/SP3

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11.February.2014