MCSA/MCSE Self-Paced Training Kit (Exam 70-270): Installing ...

4-20 Chapter 4 Modifying and Troubleshooting the Startup Process
The CurrentControlSet subkey is a pointer to one of the ControlSet00x keys. The Clone
control set is a clone of the control set used to initialize the computer (either Default
or Last Known Good), and is created by the kernel initialization process each time you
start your computer. The Clone control set is not available after you log on.
To better understand control sets, you should know about the Registry subkey
HKEY_LOCAL_MACHINE\SYSTEM\Select. The entries contained in this subkey
include the following:
Current Identifies which control set is the CurrentControlSet. When you use Control
Panel options or the Registry Editor to change the Registry, you modify information
in the CurrentControlSet.
Default Identifies the control set to use the next time Windows XP Professional starts
unless you select the Last Known Good configuration. Default and Current typically
contain the same control set number.
Failed Identifies the control set that was designated as failed the last time the computer
was started using the Last Known Good control set.
LastKnownGood Identifies a copy of the control set that was used the last time the
computer started Windows XP Professional successfully. After a successful logon,
the Clone control set is copied to the Last Known Good control set.
Each of these entries in HKEY_LOCAL_MACHINE\SYSTEM\Select takes a
REG_DWORD data type, and the value for each entry refers to a specific control set.
For example, if the value for the Current entry is set to 0x1, the CurrentControlSet
points to ControlSet001. Similarly, if the value for the Last Known Good entry is set to
0x2, the Last Known Good control set points to ControlSet002.
How to View and Edit the Registry Using the Registry Editor
Setup installs Registry Editor (REGEDIT.EXE) in the %systemroot%\System32 directory
during installation. However, because most users do not need to use Registry Editor, it
does not appear on the Start menu. To start Registry Editor, click Run on the Start
menu, type Regedit, and then click OK.
Although Registry Editor allows you to perform manual edits on the Registry, it is
intended for troubleshooting and problem resolution. You should make most configuration
changes through either Control Panel or Administrative Tools. However, some
configuration settings can be made only directly through the Registry.
Caution Using Registry Editor incorrectly can cause serious, system-wide problems that
could require reinstallation of Windows XP Professional. When using Registry Editor to view or
edit data, use a program such as Windows Backup to save a backup copy of the Registry file
before viewing. In Windows XP Professional, you can use Backup to back up the System State,
which includes the Registry, the COM class registration database, and the system boot files.