Why Undelete Utilities Fail

If you use a Windows computer regularly, sooner or later you accidentally delete an important file. Wouldn't it be great if you could just "undo" that mistake? In fact, it turns out that several companies sell products that promise to let you do just that -- to "undelete" files that you unintentionally deleted. Unfortunately, those utilities won't always help you, and this article explains why.

Doesn't the Recycle Bin Work?

If you know about the Windows Recycle Bin, you might be thinking that you can always go there to recover any accidentally deleted files. The truth is, however, that many deleted files cannot be recovered from the Recycle Bin.

First, Windows programs have to perform a special operation to move files to the Recycle Bin instead of just deleting them. Many Windows programs do not automatically offer this feature. For example, power users who work in the Windows command shell soon learn that the shell's DEL command simply deletes files -- they are not moved to the Recycle Bin.

Second, the Recycle Bin has a limited size, and as you keep deleting things, eventually some files have to get thrown away. Although you can adjust exactly how big your Recycle Bin is, there's no getting around the fact that disk space is finite. If you keep creating and deleting files, sooner or later some of them have to get thrown away.

Finally, it's also possible to configure the Recycle Bin so that it always throws away every file immediately. This effectively "turns off" the Recycle Bin, which saves you some disk space, but means that that document you just deleted cannot be simply copied back out of the Recycle Bin.

Undelete File Utilities

If the Recycle Bin fails you, then what good are these undelete file utilties? In fact, they can sometimes be very good, due to the details of how Windows manages file space.

Each Windows file is stored in one or more fixed-size chunks. Just think of your hard disk as being divided into little blocks. A little file might use up just part of a block, while a big file might use up many of these fixed-size blocks. Windows internally keeps track of where all the blocks that make up any particular file are. Obviously, Windows also knows where all the unused blocks on your hard disk are, so it can go get them whenever you create a new file.

The secret to these undelete utilities is that when you tell Windows to delete file (accidentally or not!), Windows doesn't go out and erase all the blocks that that file was using. Instead, Windows saves time by simply recording the fact that all those blocks are now unused.

That being the case, these undelete utilities can work by cleverly locating all the blocks that belong to recently deleted files in a particular folder (aka "directory") and using the data in those blocks to reconstruct your lost file(s). Sometimes, they need a little help from you to figure out what files you are trying to recover, and sometimes the recovered file is not 100% perfect. Many times, however, the recovery is 100% perfect and the undelete utility works just like magic!

The Real Problem

So when is it that undelete utilities don't work, and why do I claim that they may not work for you? The problem goes back to how these utilities work.

Suppose you just accidentally deleted a file that was using up 30 of those fixed-size blocks of disk space I was talking about. However, instead of immediately reaching for your undelete utility, suppose that you do some other work on your computer before realizing you've deleted the wrong file. Well, if you do anything that creates a new file or grows an existing file, Windows will have to go out and grab some blocks from the pool of unused disk blocks and write over them with the new data being created. If Windows happens to choose one of the blocks from the file that you later hope to "undelete", then you're out of luck!

Think of this like dropping a contact lens at a party. Dropping the lens probably didn't hurt it. If you yell "Nobody move! I dropped my contact lens!", then everybody can freeze, carefully bend over, and probably locate and pick up the contact lens without any problem. However, if you drop your contact lens and the party goes on for 15 minutes before you notice, the odds go up that someone will have destroyed your lens by stepping on it.

You're probably thinking "I know pretty quick when I deleted the wrong file, so that won't be a problem for me!" But now I get to the real Catch-22 of why undelete utilities may not work when they're needed most.

You Gotta Buy It Before You Need It

Here's the catch. Most people don't buy an undelete file utility until the day when they actually just deleted that important file. Undelete utilities are like insurance -- most people won't think to buy one until they actually get burned. That would be fine, but there's a technical problem with that.

Remember that the more work you do on your computer after you accidentally delete a file, the lower the odds that the undelete utility can get your data back safely. But how exactly are you going to purchase and download that undelete file utility? Downloading a file obviously creates new data on your disk, and could overwrite your undeleted data. But even just browsing the web to locate a utility causes new temporary files to be created -- another threat to your data.

Even if you carefully step away from your computer, go to another machine to locate, purchase, and download an undelete utility, you still have to bring it back to your first computer and install it there. Again, the act of installation can overwrite some of the data you are hoping to recover.

Now you can see the Catch-22 of file undelete utilities: just when you need them most, there's a fair chance they won't work for you because the activity of purchasing and installing them can interfere with the process of recovering your lost data.

The solution is simple: buy and install an undelete utility before you need it. However, human nature being what it is, most people won't do that. We don't buy snow shovels before the big snowstorm hits, we don't get religion about backing up data until the hard disk crashes, and we just can't seem to make ourselves buy undelete utilities until we just deleted something very valuable!

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