What happens to trash backup files?

When you move a file to trash it simply moves the filename/etc to the 'trash' folder. This is the same as moving it from one folder to another. When you empty the trash the space for the file gets released back to the system and the file name entry in the table is usually just marked 'deleted'. If you have, for example, a file on a thumbdrive and move it to the trash then dismount the thumbdrive, you can't delete it since the system cannot access the thumbdrive to complete the delete. Also the thumbdrive will still show the space as not available. They do not make copies of the files. There are some type of secure delete which actually wipe the data, but this takes time, especially with a large file, so usually they don't bother. This of course implies that if you were to use a a program that could read individual sectors on the disk you could possibly find the data, assuming it had not been re-used.

 

When you "empty" trash, All info pointing to the existence of the file is deleted. The file is there in the free space, unknown to the system now.

When new data is written, it is written over the ghost data in the free space, overwriting the file and eliminating it for good. Securely Emptying trash writes zeros over all the data I think, making it all nearly impossible to recover again.

 

I have a question, too.

If I moved a file to the tmp directory and restarted the machine, no files in the tmp directory any more. So, does this operation make a completed delete? Is it possible to recover the file again?

Thanks!

 

Go to Finder, then Preferences and then click the advanced tab. There you'll see an option that says Secure Empty Trash. That will delete your files completely when you empty the trash!