The deletion of restore points may be caused by any one of the following by-design conditions:
You run out of disk space on the system drive or on any one of the available non-system drives, and System Restore stops responding and stops monitoring your system.
This behavior causes the system to delete all restore points in an attempt to free up disk space. However, you have probably already received a warning about running low in disk space prior to this point. In this case, when sufficient disk space is freed, System Restore starts to monitor the system again. At this point, it creates an automatic System Checkpoint.
Note If you have a multiple-partition computer with a drive that has almost no free space, this drive may cause System Restore to stop responding all across the system and to delete restore points. However, this only occurs if you have reached the minimum disk space that is allowed and if you perform operations on monitored file types. Examples of such operations are upgrading, uninstalling or installing programs, moving, and deleting or renaming files. If your drive has almost no free space but you only perform operations on non-monitored files, System Restore does not stop responding.
You manually turn System Restore off.
If you manually turn System Restore off on the system drive, all restore points are deleted, and you receive the following warning message:
You have chosen to turn off System Restore. If you continue, all existing restore points will be deleted, and you will not be able to track and undo changes to your computer.
Do you want to turn off System Restore?
If you manually turn System Restore off on any non-system drive, all restore points on that specific drive are deleted, and you receive the following warning message:
You have chosen to turn off System Restore on this drive. If you continue, you will not be able to track or undo harmful changes on this drive.
Do you want to turn off System Restore on this drive?
When you turn System Restore on again on the system drive, it immediately creates a System Checkpoint. When you turn System Restore on again on a non-system drive, it does not immediately create a restore point on that drive, but monitoring resumes immediately on the drive.
You upgrade from one operating system to another or you reinstall the operating system. The upgrade might be from Microsoft Windows Millennium Edition to Windows XP or from Windows XP to Windows XP.
After you run the Setup program, you will have to run System Checkpoint, but the restore points you had under the previous operating system are gone. Windows does not let you return to an older version of the operating system by using System Restore.
Note When you upgrade, you might still see some restore point files and folders in the <drive letter>:\System Volume Information in Windows XP or under the <System Drive>:\_RESTORE folder in Windows Millennium Edition. However, these restore points are obsolete and cannot be used as they do not appear on the Select a Restore Point list on the System Restore page.
If you start the Disk Cleanup utility and you click the Disk Cleanup tab, a System Restore: Obsolete Data Stores entry is available. These are files that were created before Windows was reformatted or reinstalled. They are obsolete and you can delete them. If you choose to clean up and delete these files, you will no longer see them under the folders that are mentioned earlier in this article, and the option to delete obsolete data stores will no longer appear on the Disk Cleanup utility.
You start the Disk Cleanup utility, click the More Options tab, and then click Clean up under System Restore. When you do this, all restore points (except the most recent one) are deleted.
You are running low on disk space, but not so low that System Restore stops performing. System Restore deletes some of the restore points, but not all of them. This occurs because System Restore uses a First In First Out (FIFO) process to decrease the size of the data store to approximately 75 percent of its maximum size when the data store reaches approximately 90 percent of its maximum size. The maximum size may be the default size, or it may be set by the user. System Restore performs this deletion regardless of how much disk space you have.
A restore point reaches an age of 90 days. The restore point is then deleted because 90 days is the default time to live.
You manually reduce the data store size. This triggers the FIFO process to delete some restore points to accommodate the newly-resized data store.
System Restore uses the FIFO process on restore points consistently across drives and always deletes full restore points. System Restore keeps restore point information about all drives. So when one drive causes System Restore to use the FIFO process on restore points because of low disk space, the restore point information is deleted on all drives.
For additional information, see the following Microsoft Knowledge Base articles: