For once, I am not in dire need of assistance, I was just wondering if anyone knew this. Just out of curiosity.
I now know that files are never really deleted, unless someone uses specialised applications to do so. They are stored in your HDD where the OS can't have access to.
If, for example, you delete something out of your trash bin. I know it is queued back into usable storage space for any new file, but does anyone know how this process works and how much time it takes (or how much data needs to be used) in order to overwrite any previous data?
In Windows delete, the filename changes and is flagged to allow the sector(s) to be over-written by new data, but stores the new name in the MBR. At that point it can be retrieved through Windows recycle bin, or through other, similar software. It will stay there and be available for restoring until other data overwrites the sector(s), you restore it, or when other deletions reach your recycle bin capacity.
To ensure the data is really deleted, you can use various secure shredder software, e.g., Spybot S&D has a utility for deleting files that overwrites the files several times, which makes it unrecoverable, there are other utilities that also do this.
To securely erase an entire HDD, you can use the mfr's. utility software to write 0's and 1's to every sector of the HDD.