Volume Shadow Copy Technology
Volume Shadow Copy Technology (VSCT), which is enabled by default, allows backups to be made files even when they are currently locked and in use. Volume shadow copies are only created for NTFS volumes running under Windows XP Professional. There must be enough free disk space available on any available local NTFS volume for the shadow copy to be made.
Whenever a backup procedure begins, an instant shadow copy of the volumes being backed up is created. The Backup program can then back up all of the files from the shadow copy rather than from the original volume. Once the copy has been created it does not change, even if data on the original volume is altered while the backup is running. Once the backup is complete, the shadow copy is deleted.
VSCT allows applications and services to be backed up while they are running. Open files appear closed on the shadow copy and the data within them files is frozen as of the time that the shadow copy is created. However, open files on the original volume remain open and their data may continue to change.