It lurks inside every computer, but unless it’s causing trouble it seldom draws attention to itself.  Your hard drive is the workhorse of your computer, but do you really know what it’s doing in there?

Here’s a brief description of how your hard drive works, and what you can do to make sure it keeps working the way it’s supposed to.

how it works
When you save a file to your hard drive, the binary language of electronic language (all those ones and zeros) is translated into a series of magnetic impulses, positive and negative, and recorded onto a round, rigged platter inside your hard drive. These platters are typically made of aluminum or glass, and most hard drives have several of them mounted on a spindle that allows them to spin as fast as 15, 000 times per minute, though more typically between 5,400 and 7,200 times per minute.  Each platter has two read-write heads, one for each side, mounted on a single arm with a slider that allows the heads to move back and forth across the surface of the platter to access data. 

The amount of data each platter can hold is determined by its areal density (sometimes called bit density), which is usually measured in gigabits per square inch.  TPI, or Tracks Per Inch, is another measurement of disk capacity, where a track equals one concentric ring around a disk.  While a 3.5-inch floppy disk has a TPI of 135, a typical hard disk has a TPI in the thousands.  Because of the vast amount of data that can be stored in a single track, each track is further divided into sectors.  A single sector holds about 512 bytes of information.  When you save data to the disk, it is referenced according to its track and sector.

defrag your hard drive
If you’ve opened a file recently, it might be stored in your hard drive’s cache (or buffer), and can be accessed again with lightening speed.  Unfortunately, the cache on a hard drive is usually limited to 4 MB or less, and your hard drive must in most cases search the disks for the data you’ve requested.  Because data is generally not stored in sequence on the disks, but stashed wherever space is available, this can take some time.  The whirring sound your hard drive makes as it searches for a file is the sound of the platters spinning as the read heads zoom back and forth to access each sector where the data has been stored.

You can speed up this process by periodically defragging your hard drive.  The Windows Disk Defragmenter utility will reorder the scattered data on your hard drive, increasing the speed with which files can be accessed. 

To run Disk Defragmenter in Windows 98 and Windows Millennium, follow these directions:

1. Shut down all applications.  The utility takes several hours to run, so pick a time when you won’t need your computer.     
2. Click on Start  > Programs > System Tools > Disk Defragmenter.     
3. Select the drive you'd like to defrag and click “Settings” button.     
4. On the Disk Defragmenter Settings menu checkmark "Rearrange program files so my programs start faster" and "Check drive for errors." Hit OK to go back to the first screen.     
5. Click on OK to begin.

Clicking on “Show Details” will display a graphical representation of the utilities progress.

disk clean up
Another powerful utility that comes with Windows is Disk Clean Up.  This application allows you to easily sort through and delete unused and temporary files, freeing space on your hard drive and speeding up its operation.

To run Disk Cleanup in Windows 98 and Windows Millennium:

1. Go to Start > Programs > Accessories > System Tools and select Disk Cleanup.     
2. Choose the drive you want to scan from the drop-down menu, and wait while the program calculates how much disk space is available for cleanup.     
3. On the Disk Cleanup tab, check the boxes next to the type of files you want to remove.      
4. Temporary Internet Files are web pages stored on your hard drive for quick access.  Deleting these files will leave your Internet browser preferences and bookmarks intact.     
5. Downloaded Program Files are Java an ActiveX applications downloaded from the Internet to view certain pages.     
6. The Recycle Bin contains files you have deleted from your system.  They are not permanently removed until you empty the Bin.     
7. Temporary Files are created by some applications to temporarily store data.  Typically, the data is deleted when the program closes, and it is safe to delete these files if they have not been modified in over a week.
   Clicking on the View Files button will display the files to be deleted in separate window.     
8. To remove Windows components or unused programs, click the More Options tab. Clicking the appropriate “Clean up…” button will open the Add/Remove Programs utility, where you can select what you would like to delete.

scan disk
If you’ve ever turned off your computer without properly shutting down the system – or had to restart after a crash – you have probably seen your computer run a utility called Scan Disk.  Scan Disks checks the hard drive for errors and, when it finds them, marks the cluster of sectors containing the error as unusable – no data can be written to or read from that portion of the disk.

You can also run ScanDisk from within Windows, which allows you to do a more thorough scan of your hard drive and detect errors that might make it difficult to read or write to the disk, if not impossible.

To run ScanDisk in Windows 95, Windows 98 and Windows Millennium:

1. Click on Start > Programs > Accessories > System Tools > ScanDisk     
2. Select “Thorough” under Type of Test.     
3. Click Start to begin the scan.

ScanDisk should take only a few minutes to run, and should probably be done every two or three months. This will give you a report on the number and types of errors it found, and can even repair some of the errors it finds automatically.  More serious errors can be repaired by reformatting the drive, if the errors are those known as “soft’ errors, meaning the magnetic signal on the disk is weak or the formatting is messed up.  “Hard” errors, however, refer to actual physical damage to the disk, such as a scratch or a bump, and cannot be repaired.  If you have a large number of hard errors on your disk, you will probably need to replace your hard drive.

The average life span for today’s hard drive is between three and five years.  Simple maintenance can keep your drive running smoothly well past the time it’s become obsolete.