The Registry

1. The Registry 4 February 2004

2. The Registry • A hierarchical database containing information • Hardware • Software • Device drivers • Network protocols • User configuration needed by the OS and applications

3. Components That UseWindows XP Registry • Setup programs for devices and applications • User profiles maintained/used by OS • Files active when Ntldr loading the OS • Device drivers • Hardware profiles • Application programs

4. Setup Programs For Devices/Apps • Record configuration information in the registry • Query registry for information needed to install drivers and applications

5. User Profiles Maintained &Used by the OS • Maintains user profiles that determines environment • Kept in files but written to registry when user logs on • Changes recorded to profile and rewritten to file when user logs off • OS uses this information to control user settings and other configuration settings for this specific user

6. Files Active When Ntldr IsLoading The OS • During boot process, NTDetect.com surveys hardware devices present • Records the information in registry • Ntldr uses info from registry to load & initialize drivers for these devices • Includes the order in which to load them

7. Device Drivers • Read & write info to and from registry each time they load • Drivers write HW configuration info to the registry • Read it to determine proper way to load

8. Hardware Profiles • Windows can maintain multiple sets of HW configuration info called hardware profiles on one PC • Data kept in the registry • Example: Notebook with docking station • Two profiles: one docked & one undocked

9. Application Programs • Many apps read registry for info about the location of files the program uses • Various other parameters that were stored in the .ini files under Windows 9x

10. How The Registry Is Organized • Two ways to look at the registry • Physical Organization • Logical Organization

11. Logical Organization of the Registry • Looks like upside-down tree • Five branches called keys or subtrees • See Fig. 10-11 p. 433. • Categories of information stored in registry • Each key made up of subtrees • Those subtrees made up of other subtrees • Last subtrees made up of values

12. Logical Organization of the Registry • Values are lowest level on the tree • Each value has a name and data assigned to it • Data in registry always stored in values

13. Registry Editor • Opens a Windows Explorer-type window • Shows you five keys in the registry • HKEY_CURRENT_USER • HKEY_CLASSES_ROOT • HKEY_CURRENT_CONFIG • HKEY_USERS • HKEY_LOCAL_MACHINE

14. HKEY_CURRENT_USER • Information about the currently logged-on user • Printer settings • Desktop settings • Anything set for the current user

15. HKEY_CLASSES_ROOT • Information about software and the way software is configured • Points to data stored in HKEY_LOCAL_MACHINE

16. HKEY_CURRENT_CONFIG • Information about the active hardware configuration • Extracted from data stored in HKEY_LOCAL_MACHINE subkeys SOFTWARE and SYSTEM

17. HKEY_USERS • Information used to build the logon screen and ID of currently logged-on user

18. HKEY_LOCAL_MACHINE • All configuration data about the computer • Information about device drivers and devices used at startup • Information in this key does not change when different users are logged on

19. Physical Organization of the Registry • Quite different from logical organization • Physically stored in five files called hives • No one-to-one relation to the subtrees, even though there are five of each • See Fig. 10-13 p. 425.

20. HKEY_LOCAL_MACHINE • Stored in four hives • SAM hive • Security hive • Software hive • System hive

21. HKEY_CURRENT_CONFIG • Data kept in portions of two hives • Software hive • System hive • Subtree uses data stored in the HKEY_LOCAL_MACHINE subtree

22. HKEY_CLASSES_ROOT • Data kept in a portion of the Software hive • Subtree uses data stored in the HKEY_LOCAL_MACHINE subtree

23. HKEY_USERS • Kept in the default hive

24. HKEY_CURRENT_USER • Kept in a portion of the default hive • Is a subset of the data in HKEY_USERS subtree

25. Physical vs. Logical • Don’t let physical configuration cloud view of the logical organization • Even though some data is subset of other data, no subkey is subordinate to another in the five subkeys • Registry hives stored as a group of files in \%SystemRoot%\system32\config folder • Physically, each hive is a file, backed up with logfile in same folder

26. Editing The Registry • Registry is modified automatically when changes made in • Control Panel • Device Manager • Many other places in Windows NT/2000/XP • Usually that is all the change ever needed • Rarely, at the direction of Microsoft tech support, manual changes are necessary

27. Editing The Registry • This might include removing references to viruses or worms • Changes are immediate and permanent • Always back up the registry before you make any changes, in case something goes wrong! • When you do a backup of the system state after an installation, you also make a copy of the registry

28. Editing The Registry • Two editors • Regedit32.exe • Each key shown in separate window • Used to edit the registry • Regedit.exe • All keys shown in same window • Used to view the registry • Similar look and feel as Explorer