It will take longer time to read a whole file when it is fragmented, because the HDD has to make several seeks to read all the cluster-chains that contains the file. Defragmentation Tools will try to rearrange the data of the fragmented files so the file is contained in a single cluster-chain.
Checks before starting defragmentation of a partition :
- Scan the partition for errors (Using Scandisk or Chkdsk /f).
- Empty directory with temporary files which might reside on the partition (Recycle Bin, Temporary Internet Files, TMP).
- Make sure there is enough free space on the partition to move files around (15 %).
- Stop any unnecessary programs that writes to the partition (Ex. filesharing programs).
- Disable any screen saver which might take all the resources from the defrag process.
Note a new feature was added with Windows 98/Windows XP, which monitors the launch of applications. The defragmenter uses this information to group the files used by the application close together to minimize seek time.