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The Care and Feeding of Hard Disks

Hard disks are not as vulnerable to dust and liquids as floppy disks are, because they are sealed inside metal cases. They are, however, far from indestructible. Knocking a computer off your desk or dropping it on the floor is a sure-fire way to lose some data, if not permanently damage the disk. Some hard disks are more sensitive than others and may respond poorly to being repeatedly moved from desk to desk.

Caring for Your Hard Disk

The basic rules of thumb for caring for a hard disk are

  • Don't drop your computer.

  • Unless you have a laptop or other computer designed for travel, don't move it any more often than you have to.

  • If you're relocating to another office or building, try to pack the computer in its original packing materials to cushion it during the move.

  • Most important, back up your data regularly. Operate on the assumption that sooner or later, your disk will fail (probably a day or two before some crucial deadline).

How Hard Drives Work

Most hard drives spin at thousands of revolutions per minute. While the disk is spinning, the read/write heads on hard disks hover above or below the disk's surface, at a distance of millionths of an inch. (To make it a little more concrete, the distance between the read/write heads and a spinning disk is less than half the width of a particle of smoke.) When your computer is turned off, the read/write heads do come to rest on the surface of the disk, but only within a specified parking area that is reserved for this purpose and is never used for storing information.

Hard Drive Malfunctions

If your hard drive malfunctions for some reason or you drop your computer on the floor, the read/write heads may fall onto the disk, permanently damaging it. This event, which is actually quite rare in modern-day hard drives, is known as a head crash. If someone tells you that their hard disk "crashed," they probably mean it underwent a head crash.

The Gap Between the Read/Write Head and the Disk

The small but essential gap that exists between the surface of the disk and the read/write heads explains why hard disks always live inside sealed containers, safe from such hazards as smoke, dust particles, and soda pop. Because the distance between the disk and the read/write head is half the size of a smoke particle, any encounter with such a particle would be like a high-speed go-cart running into a boulder.

Figure 3.15

Fragmented Files

I've been representing each file as occupying a single discrete area of a disk. In reality, files are usually stored in segments scattered across the disk. The first part of a file may be wedged in between two other files, for example—perhaps in the space previously occupied by a file you later deleted. Because the whole file cannot fit in that space, your computer makes a note of where the next piece is stored (rather like the next clue in a treasure hunt). If there isn't enough room for the rest of the file in that second spot, your computer makes a note of where the third piece is stored, and so on. Files stored in this way are said to be fragmented.

Figure 3.16

Defragmenting Your Hard Disk

Over time, your hard disk will accumulate many fragmented files (files stored in clusters scattered across the disk). Every time you load one of these files into memory, your computer has to jump from one part of the hard disk to another, collecting all the file's different pieces. You can improve your computer's efficiency by periodically defragmenting your hard disk—that is, running a special program that rearranges data so all the parts of each file occupy contiguous areas (clusters) on the disk. (You can compare this process to a bunch of people trading seats so a group of friends can sit together.)

The Disk Defragmenter Utility

Windows has built-in utilities for defragmenting a hard disk; look up defragment in the Help system for details. (You'll learn how to use the Windows Help system in Chapter 5.)

Using ScanDisk

Windows' ScanDisk utility allows you to search for and clean up errors on your hard disk that are causing problems or taking up space. ScanDisk is accessed from the Start menu's Accessories menu.

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