PerfectDisk's Online defragmentation defragments the drive when the computer is ON and running. The defragmentation pass runs in the background without disrupting your work. Since online defragmentation runs when the system is ON, it does not defragment system files and directories (FAT 16/ FAT 32/exFAT), which requires Boot time (Offline) Defragmentation (System Files only).
The following topics are covered to help you understand and run Online defragmentation:
§ Pre-configuring Online Defragmentation for Best Performance
§ Manually Running Online Defragmentation
§ Scheduling Online Defragmentation
§ Configuring Automatic Modes of PerfectDisk for Defragmentation