Recovering, deleting, retrieving files

  • By Sven Mogelgaard and Will Rutherford Tech Talk
  • Tuesday, April 29, 2008 11:05am

Three of the more frequent questions we hear are, “Why can’t you recover my lost file(s)?” “How do I securely delete data from my hard drive?” and “Why does it take so long to open and save files?”

The answers to these questions are all tied to your computer’s hard drive. Understand how today’s hard drives save and retrieve data and you will find the answers to such questions.

In general terms, your hard drive is made up of several disks called platters, which are stacked one on top of the other and connected to a central axle called a spindle. An arm with a read/write head on its end extends across the flat side of the platter and moves back and forth. (Imagine an old-fashioned record player where the record is the platter and the needle is the read/write head.) The platters spin at several thousand revolutions per minute. The heads float within a thousandth of an inch above the platter and read and write data on the platters as they spin.

Now it gets interesting. Let’s look at how your computer writes data to the hard drive. When I click “Save” as I write this article, my laptop sends bits and bytes that make up this document to my hard drive. The read/write heads deposit these bits and bytes onto the platters of my hard drive into the first open space it finds. Simple enough. But what happens if the open space isn’t big enough to hold all the bits and bytes of my article? And how does it know space is open in the first place?

A special file on your hard disk (called the file allocation table, or FAT) keeps track of what is stored on your hard drive and where it is written. So in this example, when I save this article, the hard drive finds an open spot on platter two and starts writing data there.

But the hard drive doesn’t know how much space is needed to save the article. It isn’t unusual for your hard drive to start writing data only to run into a chunk of data belonging to another file. When that happens, the hard drive looks for the next open area. That may be on platter four. This process continues until the entire article is saved. The location of each piece of my article is stored and duly recorded in the FAT. The next time this file is opened, my computer will use the FAT to find the pieces of my article and reassemble them into a Word document I can review and send off to my editor.

Let’s tie all this together and answer our three questions. First, let’s look at why it can be difficult to recover lost files. When you delete a file and empty the Recycle Bin, the entry for that file is deleted from the FAT. Without the information in the FAT, Windows does not know how to find and reassemble your file. Notice we said the FAT entry was deleted, not the file itself. However, recovering that file will require special software and may or may not be successful. And if you’ve done anything that writes data to the hard drive you may have overwritten some or all of your file.

The fact that a file’s data is never really deleted makes it difficult for the average user to ensure potentially sensitive data is gone. To truly erase data, the file’s data must be written over with random data one or more times. Companies like Acronis and Webroot sell commercially available programs to erase your data to U.S. Department of Defense standards, and your favorite Internet search engine will list thousands of others claiming to do the same thing.

What does all of this have to do with files that open and close slowly? It has to do with the way files are written in pieces to multiple locations on the platters of the hard drive. This is called fragmentation. As files are saved in more and more pieces, or fragments, it takes longer and longer to open or save these files. A badly fragmented drive can make working on your computer a very frustrating experience.

Fortunately Windows provides a tool called the Disk Defragmenter, which moves all the file fragments around so that all the pieces for each file are put together in one location.

Note that it can take anywhere from a few minutes to several hours to defragment your drive, and it’s best not to use your computer while the defragmentation process is operating.

Sven Mogelgaard is the owner of Mill Creek-based Byte Slaves Inc. ( and can be reached by calling 425-482-9529. Will Rutherford is the owner of Bothell-based Computer Concepts ( and can be reached by calling 425-481-3666.

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