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Stop Hard Disk Thrashing
By Stephen Bucaro
Hard Disk Thrashing is when your computer's hard disk activity light stays on, and you hear your
disk spinning most of the time, even when you're not doing anything on your computer. When you do
try to do something on your computer, it responds very slowly. Something is working your hard disk
real hard, and it's not you.
Virus or Spyware
The first culprit to suspect is a virus or spyware. Make sure your antivirus program's definition
files are up-to-date and run your antivirus program. If you don't have an antivirus program installed
on your computer, you can use Trend Micro's
free online virus scanner, or download
AVG Anti-Virus Free Edition.
Similarly, make sure your anti-spyware program's definition files are up-to-date and run your
anti-spyware program. If you don't have an anti-spyware program installed on your computer, you can
use Trend Micro's free online spyware
scanner, or download Lavasoft's
free Ad-Aware Personal edition spyware remover.
Fragmentation or Bad Areas
You can visualize your computers hard drive as a disk with data stored as tiny magnetic fields. Data
is stored in concentric circles called "tracks" that are divided into pie shaped sections called "sectors".
Data is stored in a number of adjacent sectors defined as an "allocation unit". A read/write head hovers
above the spinning disk. To store a file, the read/write head will place parts of the file in "free"
allocation units. Unfortunately, except for on a brand new disk, the parts of the file will NOT be stored
in adjacent allocation units.
Disk before fragmentation
After file B is deleted and file D added, file D is fragmented
As you add and delete programs and data from your hard disk, non-adjacent allocation units become
free. Parts of files are stored in any free allocation units, not necessarily adjacent, that the
read/write head finds. This results in parts of files being scattered all over the disk. This is called
"fragmentation". Having a fragmented disk means when you load a program or data, the hard drive must
search all over the disk for parts of the file. If a disk is badly fragmented, the result is disk thrashing.
It may surprise you to learn that few, if any, hard disks are perfect as they come off the
production line. They all have bad areas. When the manufacturer low-level formats the disk, the bad
areas are cordoned off by demarking them with special code. Even after a disk is put into service,
an area of the disk may go bad. Modern operating systems can detect when an area of the disk is
becoming unreliable and will automatically relocate the data stored there, and cordon off the bad area.
If a disk has too many bad areas, the result is disk thrashing.
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