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About System Restore
- System Restore monitors system changes and saves the system state as a restore point. If a system problem develops as a result of a system change, the user can return the system to a previous state using the data from a restore point.
Applications and the system can create restore points when system changes occur. System Restore also creates checkpoints every 24 hours of absolute time. In addition, users can create manual restore points at any time.
- System Restore does not restore user data or documents, so it will not cause users to lose their files, email, browsing history, or favorites. System Restore is also made available to users in safe mode, making it easier for them to restore their computers to a state before problems occurred. Note: restoring a system from Safe Mode or from the Command Prompt an Undo restore point will NOT be created!
Monitoring the System
- System Restore monitors and restores a core set of system and application files, archiving the states of these files before system changes are made. System Restore also saves a snapshot of the registry (note: some current registry values will persist) and some dynamic system files. When System Restore detects that the user is not actively using the computer, (Idle time) it compresses the registry and any file copies made.
- System Restore requires a minimum of 200 MB of free disk space on the system drive at installation. When the amount of free disk space falls below 50 MB on ANY monitored drive, System Restore switches to standby mode and stops creating restore points. All restore points are deleted at that time. System Restore reactivates and resumes creating restore points as soon as 200 MB of disk space is free on the system drive.
- The files that are monitored or excluded from monitoring are specified in the file %windir%\system32\restore\Filelist.xml. For more information, see Monitored File Extensions.
Restoring the System
- As the computer is used over time, restore points are collected in the data archive without any management or intervention required by the user. If the user ever needs to restore the system to a previous state, the available restore points are made visible to the user through the System Restore user interface. The user can choose any available restore point. The only recommended way to access this archive of restore points is through the System Restore user interface and the System Restore API; this is to protect data integrity and prevent accidental changes made by the user, applications, or other agents.
- To restore a system, System Restore undoes file changes made to monitored files, recapturing the file state at the time of the selected restore point. It then replaces the current registry with the one saved for the selected restore point.
- To ensure that your application has the desired behavior after a restore, do the following:
- Ensure that key application binaries to be protected use extensions consistent with those used in Filelist.xml. For more information, see Monitored File Extensions.
- Do not use monitored extension types for user-editable files. For example, if you name a user's personal data file using the extension .ini, the user may lose work as a result of a system restore.
- Do not store information in the registry that prevents user access to personal data files or applications on system restore. Otherwise, you must provide a mechanism by which the user can download and reinstall the applications without having to pay for them again.
- Use the System Restore API to create meaningful restore points at install and uninstall.
Restore Points
- Restore points are created to allow users a choice of previous system states. Each restore point contains the necessary information needed to restore the system to the chosen state. Restore points are created before key changes are made to the system.
- System Restore has an automatic restore point space-management feature that purges the oldest restore points to make room for new ones, while still enabling the user to recover from any recent destructive changes. Restore points over 90 days are purged automatically by default. System Restore takes a maximum of 12 percent of the disk space in systems with hard drives over 4 gigabytes (GB), and a maximum of 400 megabytes (MB) for hard drives under 4 GB. To reduce the maximum storage limit, use the System application in the Control Panel.
- The following describes the triggers that cause System Restore to create a restore point.
Event-triggered restore points
- System Restore automatically creates a restore point before the following events:
- Application installation (provided the application utilizes an installer that is System Restore compliant, most applications are not compliant, so create a manual restore point before installing any new software). If the application install causes system problems, the user can restore the system to a state before the installation of the application, but only after uninstalling the application via add/remove programs in Control Panel.
- AutoUpdate installation. AutoUpdate provides an easy way for users to download critical Windows updates. After the update is downloaded, the user can install the update on the system. If the user chooses to install the update, System Restore creates a restore point before the installation of the update begins.
- System restore. For example, if a user accidentally chooses the wrong restore point, the user can UNDO the restore operation by choosing a restore point before the system restore took place. The user can then choose the correct restore point. Warning: When restoring a system from Safe Mode or from the Command Prompt an UNDO restore point will NOT be created!
Scheduled restore points
- System Restore provides users with the ability to restore the system to its state on a specific days or time. It does this by creating a restore point every 24 hours. These restore points are saved and compressed, and these choices are available to the user through the System Restore user interface. Users can also manually create and name a restore point at any time from within the System Restore user interface.
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