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Rework System Restore

January's "Gunk Busters" described how to reset the disk space Windows reserves for its System Restore points (scroll to "Whip Disks Into Shape"). But the truth is, the amount of space Windows uses for restore points is a little more complicated than a single percentage value. The Registry includes its own setting for the maximum disk space given to System Restore, and Windows uses whichever amount is larger: the percentage you specify via the System Properties dialog box, or the Registry's maximum value. Any disk space you free up via System Properties won't instantly be used by System Restore; it will be available until a new restore point requires more space than the amount allotted via the percentage value. The percentage and max values tell Windows only when to stop making new restore points.

To lock in your System Restore allocation, open the Registry Editor and navigate to HKEY_LOCAL_MACHINE\SOFTWARE\ Microsoft\Windows NT\CurrentVersion\SystemRestore. Select the SystemRestore icon in the left pane to see several icons appear in the right pane. Do not experiment with just any of these icons! While you can safely change the value of some of them, Microsoft warns that others should not be altered under any circumstances. Fortunately, you can safely edit the values for the DiskPercent and DSMax icons, which control System Restore's disk-space allotments. To change the maximum amount of disk space System Restore will use (providing it's larger than the percentage value), double-click the DSMax icon. In the Edit DWORD Value dialog box, click Decimal so you can see the specified number of megabytes in the 'Value data' box (the default on most systems is '400'). Change this to the desired amount, and click OK.

While you're there, you can also safely edit the DSMin value, which specifies the minimum space System Restore needs to work at all. Normally, if free space on your Windows drive gets too low, System Restore shuts down and makes no restore points until you have at least 200MB of free space. Setting this value determines the amount of disk space at which System Restore will wake up and attempt to start saving restore points again. However, just because System Restore will try to do so, it won't necessarily succeed if the available space is too small. Unfortunately, we know of no method to determine how much space a single restore point will require, so setting this amount too low could render the feature useless. Still, you can fit a lot of system files in 100MB of disk space.

To change this value, double-click the DSMin icon, click Decimal, and enter your desired amount of free disk space (in megabytes) in the 'Value data' box (see FIGURE 6). Click OK.

Edit Registries From Afar

If your PC has multiple users, or if you have access to the right files over a network, you can use Windows XP's Registry Editor to modify not just your own Registry, but those of other accounts as well. First, log on to an administrator account and open the Registry Editor as described previously. Select the HKEY_USERS key in the pane on the left, and choose File, Load Hive. In the resulting dialog box, navigate to another user's folder inside Documents and Settings on the drive in which Windows is installed (usually C:\Documents and Settings\username, where username is the account whose Registry you want to edit). Select the ntuser.dat file and click Open (the file name may be in all caps).

Note that if file extensions are hidden on your system (which is Windows' default setting), you won't see the '.dat' extension, only 'ntuser'. In fact, if Windows' folder options are set to hide system files and folders (again, the default), you won't see this file at all. In this case, navigate to and select the account's folder in Documents and Settings and type ntuser.dat in the 'File name' field at the bottom of the Load Hive dialog box and press <Enter>.

Now you'll be prompted for a Key Name, which is the name the Registry Editor will give to the folder icon for these settings. You can enter any name you want, but using the same name as the account will help you track whose settings you are editing. When you're done, press <Enter>.

Expand the branch under HKEY_USERS\username (replacing username with the name of the key you just created) to find the setting you want to edit (see FIGURE 7). These keys will be the same as the HKEY_CURRENT_USER section when you edit your own profile's Registry settings.

When you've made your changes, select the key you added and choose File, Unload Hive. Click Yes at the warning. You can open and edit more than one account at a time, but be sure to unload the hive for each user before attempting to log on to the user's account. Otherwise Windows may have trouble loading the proper Registry settings for the account you just worked on.