My 9/14/08 Missoulian column
Hard drives are a little like the elephants of the computer world: They don’t necessarily forget things, like those documents and photos you though you deleted last week or last year.Even after you empty the recycle bin or trash on your personal computer, the files may still be on the hard drive, waiting to be found by someone else when you recycle your PC or give it away.
The reason for this elephantine habit of not forgetting comes from the early days of computers. Back then, computers filled large rooms and any task – including deleting files – took time. It was believed that those valuable seconds would be better spent crunching numbers, so the engineers came up with a solution that was – and still is – elegant in its simplicity and a time saver.
Modern hard-drive technology is incredibly sophisticated, but one of the basic most methods of organizing files remains: the catalog. Hard-drive catalogs are something like library catalogs, though much more complex. The solution for deleting files that engineers came up with works this way: When you delete a file, instead of deleting the entire file and all of the information in it – e-mails, documents and photos – your PC only deletes the catalog entry for it.
Engineers designed hard drives this way to save processing time, because they still have to control other parts of the system while deleting the file. This is also evident when you save a large file – it can take a few seconds or more.
So, when you delete a file, the information stays on the hard drive and only the catalog entry is erased. At the time, engineers decided it didn’t matter that the information remained, because without the catalog entry the file couldn’t be easily found. If the file isn’t in the catalog, they thought, it’s as good as gone.
The critical part of the solution that makes all the difference is that when a new file is created, listed in the catalog and saved to that sector on the hard drive, the old file is written over and is truly removed.
Imagine a library full of books with a catalog to find them all by title. One day, a librarian decides it’s time to get rid of some old books no one reads. Instead of spending time locating the books and taking them off of shelves around the library, the librarian removes the title of the book from the catalog. Without the title in the catalog, no one will know the book is in the library, he figures.
When new books arrive and the library needs space on the shelves, the old books are discarded. In the meantime, you can still find the old books without using the catalog, by checking each shelf, book by book.
Software that salvages deleted files on your hard drive works the same way: It finds the catalog entries that are marked as free space and reads them anyway, locating the old files. It can be used to rescue files from a crashed hard drive and sometimes even files that have been overwritten by new information.
This same software can find files on other people’s hard drives. Last year, a news story circulated about students at a California technical school who were working on their senior thesis. They went to a local thrift store and bought old PCs and, using readily available file recovery software, found all kinds of private information on the hard drives. It included the usual documents and photos, but also Web histories and stored passwords for for banks and on line retailers.
There are ways to truly erase your hard drive before you recycle it or give it away. The Montana Department of Environmental Quality has information on hard drive wiping software. A program called Darik’s Boot And Nuke seems to be the most popular. Or check DEQ’s list for computer recyclers for recyclers in your area and ask them about erasing your hard drive when you recycle.
So erase or arrange to have your hard drive erased before you recycle or give away your PC. And know that USB and “flash” drives work in the same elephantine way – they don’t necessarily forget, either. If necessary, however, smashing them with a hammer is a crude way to make the files on them unrecoverable.