The System Backup is automatically performed every day on all hosting accounts. System backups are kept for at least seven days, and you can choose to restore from any day going at least seven days back.
The Personal Backup is only made upon your request. You can create a Personal Backup from the Backup section in the Control Panel. When you make a Personal Backup, it is kept on the server for three days by default, but you can choose to save it permanently in your user space. If you do this, it is kept until you delete it.