System Restore is a component of Windows that you can use to restore your computer to a previous state, if a problem occurs, without losing your personal data files (such as Microsoft Word documents, browsing history, drawings, favorites, or e-mail). System Restore monitors changes to the system and some application files, and it automatically creates easily identified Restore Points. These Restore Points allow you to revert the system to a previous time. They are created daily and at the time of significant system events (such as when an application or driver is installed).
As Microsoft also documents, Windows automatically removes the Restore Points from your computer when the free space falls below 50 MB on any drives. As a consequence, because some wiping operations (such as the scrambling of file properties – name, date, size, etc.; or the wiping of the free disk space) result in the temporary reduction of the free disk space to zero bytes, the Restore Points will be removed from your system.
east-tec Eraser can help you protect your Restore Points from being deleted by Windows in the situations described above. All you have to do is make sure you select Protect my Restore Points from the Preferences page of Advanced Settings section.
NOTE: This option is visible on the Preferences page only on Windows XP operating systems.