This article was previously published under Q100010
WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.
A control set contains system configuration information such as devicedrivers and services. You may notice several instances of control setswhen viewing the Registry. Some are duplicates or mirror images ofothers and some are unique. This article describes how to find controlsets, which ones are important, and why.
Control sets are stored in the HKEY_LOCAL_MACHINE subtree, under theSYSTEM key. There may be several control sets depending on how oftenyou change system settings or have problems with the settings youchoose. A typical installation of Windows NT will contain four:
ControlSet001 may be the last control set you booted with, whileControlSet002 could be what is known as the last known good controlset, or the control set that last successfully booted Windows NT. TheCurrentControlSet subkey is really a pointer to one of theControlSetXXX keys. Clone is a clone of CurrentControlSet, and iscreated each time you boot your computer by the kernel initializationprocess. In order to better understand how these control sets areused, you need to be aware of another subkey, Select.
Select is also under the SYSTEM key. Select contains the followingvalues:
Current Default Failed LastKnownGood
Each of these values contain a REG_DWORD data type and refer tospecifically to a control set. For example, if the Current value isset to 0x1, then CurrentControlSet is pointing to ControlSet001.Similarly, if LastKnownGood is set to 0x2, then the last known goodcontrol set is ControlSet002. The Default value usually agrees withCurrent, and Failed refers to a control set that was unable to bootWindows NT successfully.
The most valuable and reliable control set is CurrentControlSet. Ifyou need to modify system settings in the Registry, CurrentControlSetis the best subkey to choose because you know that it is the correctcontrol set. You also know that if your modifications harm your systemconfiguration, you will still be able to boot using the last knowngood control set.
If you are not sure where to look under the control set for aparticular parameter, you can use the Find Key option under the Viewmenu of Registry Editor. Each control set contains two subkeys:Control and Services. Control contains miscellaneous systeminformation such as the size and location of the paging file. Servicescontains device driver information such as file system drivers, kerneldrives, and status information for each.