If you have any familiarity with the Windows NT based registry, you may have noticed the term HKEY_LOCAL_MACHINE used on occasion. This is a core part of the Windows registry and a vitally important component that handles much of the settings and configurations that we come to expect from a Microsoft Windows based operating system.

Also abbreviated as HKLM, the HKEY_LOCAL_MACHINE is divided in to five sub-folders and has full control over the local settings on a computer that apply to all users who are registered to that particular system. On the main Windows NT based operating systems, the HKEY_LOCAL_MACHINE is made up of just four subkeys, with an additional subkey that is created dynamically and remains volatile.

The other four subkeys include the SAM, SECURITY, SOFTWARE and SYSTEM keys. Each of these comprises the rest of the user dependant settings that are active across Windows. We can look a little deeper to see how each of the subkeys is relevant to the settings stored in the HKEY_LOCAL_MACHINE.

The SAM subkey stands for Security Accounts Manager. In this section, you’ll find the user and group database which controls who has access to Windows along with each set of individual personal settings. Theoretically, you can make edits to this part of the registry and alter the way that users interact with Windows. In practice, this is extremely complicated and extremely dangerous. It’s best to leave any such work to automated software that can tackle the registry with accuracy.

The SECURITY subkey contains all of the policy data that the system associates with Windows and the various programs and applications. You should not go in to edit this part of the HKEY_LOCAL_MACHINE, nor should you have any reason to in the first place.

The SOFTWARE subkey is a huge sprawling mass of classes and IDs that make up the main configuration data for nearly everything that is installed on your Windows system, including the core Windows files that form the actual workings of the operating system. One wrong edit here and you’ll find yourself locked out of Windows and facing a major restoration job.

When you open up the SOFTWARE subkey in the HKEY_LOCAL_MACHINE, you’ll notice a list of every vendor that has software installed on the Windows system. Under each vendor sub-tree, you’ll find a list of products and classes that coincide with the products applicable to that particular vendor. This is great for organizing the applications in to manageable sections, but still quite daunting to go in and edit manually. If you need to make a change in this part of the HKEY_LOCAL_MACHINE, you should once again consider a registry editing tool that can make the process a lot easier and a lot less dangerous in terms of the stability of your system.

Just like editing any part of the registry, it is possible and advisable to make a backup of the HKEY_LOCAL_MACHINE. This will ensure that in a worst case scenario, you can quite easily roll back your changes and revert to settings that you know work.

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