How does a formatted drive keep its data?

Question

Due to problems with windows or perhaps my Hard Drive I am going to format it, although I was reading that it is still possible to recover the data after its been formatted (which I don't need to do as I already used Knoppix to sort that out) But after its been formatted how is the data still there as why is the storage loss not visable? Surely if you filled your HD and then formatted it would remain full if the data was there (but just hiding right)

Answer 1

The data is still there, it's just that it hasn't been overwritten yet.  Once you write over those sectors, however, it is replaced with the new data.

Answer 2

Deleting and formatting a hard drive just resets the file table, telling it that it's ok to write new data over these "erased" bytes.