Appendix C: Per-Computer Settings

Overview

In Appendix B, "Per-User Settings," you learned about many of the settings that Microsoft Windows XP creates for users in the registry. These settings are in HKCU. This appendix is about the per-computer settings in HKLM.

The branch HKLM\SOFTWARE is similar to HKCU\Software. In fact, the organization of this key is almost identical. The difference is that these settings are computer-oriented; they affect every user who logs on to the computer. However, you find some settings in both places, HKLM\SOFTWARE and HKCU\Software. This is common with Microsoft Office XP and many of the policies in Windows XP, for example. Most often, when a setting is in both places, the version in HKLM has precedence over the same setting in HKCU. Only when an administrator removes the setting from HKLM (restricted users don't usually have permission to change settings in HKLM) do users' own preferences mean anything. The only exception to this rule is the file associations in SOFTWARE\Classes in both root keys. File associations in HKCU have precedence over file associations in HKLM. This order of precedence is necessary to enable users to have custom file associations.

Other branches in HKLM are unique, though. Windows XP stores the computer's configuration in HKLM\SYSTEM. The operating system's lower-level settings are in this branch, too. Lower-level settings include the configuration of the computer's network connections, device drivers, services, and so on. Windows XP also stores local security data in HKLM. Something else unique in HKLM is that it contains more links than HKCU does. Recall that links are aliases for other subkeys, and Windows XP uses links in HKLM to support features such as hardware profiles and configuration sets. This appendix describes these links so you can better understand how different parts of the registry relate to each other.

This appendix outlines the organization of HKLM, describing its interesting and useful subkeys. But by no means do I cover this root key's entire contents. Instead, I've focused on settings that you're most likely to customize or need to understand as a power user or IT professional. Also, I don't describe the hive files or how Windows XP loads them into HKLM because Chapter 1, "Learning the Basics," already covers this.