System Restore is a Windows XP service that runs automatically in the background, continually monitoring changes in files, folders, and settings that are essential to the correct operation of the operating system, while keeping a log of changes to file types defined in %SystemRoot%\System32\Restore\ Filelist.xml. At regular intervals, System Restore copies system files to hidden archives for safekeeping, taking a "snapshot" of your system?s registry as well. In addition, the system takes regular snapshots of the system state, including information about user accounts, hardware and software settings, and files required for startup. If you encounter a problem that causes Windows to become unstable, you can start the System Restore Wizard in normal or Safe Mode and roll back your system files and registry to those saved from a previous date? when, presumably, your system worked properly.

Note: You cannot count on System Restore to protect you from viruses, worms, Trojan horse programs, and other "malicious-ware". In fact, if your system contracts a virus, files stored in restore points created after that point might be infected also, and you run the risk of restoring the virus along with your system files. Use a reliable antivirus program, keep it up-to-date, and don&srquo;t open e-mail attachments unless you?re certain they?re safe.

You can create a restore point manually at any time. In addition, Windows XP creates restore points automatically whenever you take any of the following actions:

• You install an unsigned device driver
• You install an application using an installer that?s compatible with System Restore
• You install a Windows update or patch
• You restore a prior configuration using System Restore
• You restore data from a backup set created with the Windows XP Backup program

Finally, System Restore creates restore points at regular intervals, regardless of user activity: By default, System Restore creates a restore point every 24 hours if you leave your computer on. If you shut down your computer, the System Restore service creates a new restore point when you restart, if the most recent restore point was more than 24 hours ago.

System Restore settings and preferences are stored in the registry. Most of the values found here can be adjusted safely and easily using the System Restore tab of the System Properties dialog box. However, some settings can only be adjusted by editing the values stored in this registry key.

Normally, System Restore automatically creates restore points every 24 hours. To change this interval:

Hive:	HKEY_LOCAL_MACHINE
Key:	SOFTWARE\Microsoft\WindowsNT\CurrentVersion\SystemRestore
Name:	RPGlobalInterval
Type:	REG_DWORD
Value:	86,400 seconds (24 hours default.) Set it to half that value to have System Restore points twice a day. Double that value to have Restore points every two days.

By default System Restore deletes restore points after 90 days. To adjust this interval:

Hive:	HKEY_LOCAL_MACHINE
Key:	SOFTWARE\Microsoft\WindowsNT\CurrentVersion\SystemRestore
Name:	RPLifeInterval
Type:	REG_DWORD
Value:	7,776,000 seconds (90 days default.) A value of 2,592,000 seconds (30 days) should be sufficient.

You can disable user access to the XP’s System Restore application (located at Start, Programs, Accessories, System Tools, System Restore) by adjusting:

Hive:	HKEY_LOCAL_MACHINE
Key:	SOFTWARE\Policies\Microsoft\Windows NT\SystemRestore
Name:	DisableConfig
Type:	REG_DWORD
Value:	0 disable
Value:	1 enable

Note you will probably have to add both the key SystemRestore and DisableConfig.