I hope this hasn't happened to you. It's happened to lot's of people. Our resident computer expert Pierre Kerr, ac210@freenet.carleton.ca, gives this advice.

There are lot's of different kinds of computers so it's hard to give you a specific answer. However, most computers store information in more or less the same way.

On a computer disk, there is something called a directory or catalog. This holds information about the files that are stored on the disk. For example, if you have created a letter to a friend by using a word processing program and you save it with the name "LETTER", the computer will put the name LETTER in it's directory along with information about where exactly it's stored on the disk.

The disk is made up of a lot of small pieces called tracks and sectors. A track is a circle around the disk and a sector is a piece of a track. Let's say your letter was pretty long so it had to be stored on several sectors and tracks. All the sectors and tracks are stored in the directory along with it's name.

If you delete the file, most computers simply remove the directory information and the data is still on the disk. By using some special computer programs, it could be possible to "un-delete" the file by simply restoring the directory information.

Actually, it isn't even that hard. Some computers such as IBM PC's and maybe even Apple Macs don't even delete the directory information they simply change the first letter of the file name with a special character that shows it as being deleted. Let's say that your computer uses the character "$" to show it's deleted, then instead of having something called "LETTER" in the directory you'd have something called "$ETTER". To un-delete it you'd only have to change the "$" to an "L".

Of course, there is a problem with this, otherwise you'd think that you'd be able to delete files and undelete them anytime you wanted to. Here's the problem. Once a file has been deleted, if you then create a new file, the computer looks for available space and all the space that your deleted file is using is now available to be used by the new file. If after deleting "LETTER" you create another document and call it "NOTES", the new file might actually be in the same place as "LETTER" so of course your "LETTER" is now over-written.

So, if you ever delete a file by mistake, don't create any new files until you are able to undelete your old file.

Computers such as the IBM PC now come with a program called UNDELETE. If you ran this program right after deleting "LETTER" it would ask you to provide the first letter for the deleted file "?ETTER". You could type "L" or anything else, it doesn't matter, and it would re-create the file LETTER for you.

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€Richard (q.61)