Software Subtree in Hkey_Local_Machine

The Hkey_Local_Machine\Software subtree contains configuration information about all installed software that can write information in the Registry. The entries in this key apply for anyone using this particular computer, and include definitions for file associations and OLE information.

The software subkey contains, for example, the information you add when registering an application to use a specific filename extension and information added during installation of Windows-based applications.

The Hkey_Local_Machine\Software subtree contains several subkeys, including the Classes subkey, plus description subkeys for all installed software that can write to the Registry, as described in the following sections.

Classes Subkey

The Hkey_Local_Machine\Software\Classes subkey defines types of documents and provides information about OLE and filename-extension associations that can be used by applications. Hkey_Classes_Root is an alias for this subkey.

Hkey_Classes_Root merely points to Hkey_Local_Machine\Software\Classes. The sole purpose for Hkey_Classes_Root is to provide compatibility with the Windows 3.x registration database.

The Classes subkey contains two types of subkeys:

• Filename-extension subkeys, which specify the class-definition associated with files that have the selected extension.
• Class-definition keys, which specify the shell and OLE properties of a class (or type) of document. If an application supports Dynamic Data Exchange (DDE), the Shell subkey can contain Open and Print subkeys that define DDE commands for opening and printing files, similar to the OLE and DDE information stored in the Registry under earlier versions of Windows. In the following illustration, c:\windows\notepad.exe %1 is the print command, and the %1 parameter stands for the selected filename in Windows Explorer when the command is carried out.

Description Subkeys

The various Hkey_Local_Machine\Software\Description subkeys contain the names and version numbers of the software installed on the local computer (if that software writes information to the Registry as part of its installation process). User-specific information about the configuration of an application is stored at the same relative path under Hkey_Current_User.

Important

The information in each subkey is added by the related application. Do not edit entries in these subkeys unless directed to do so by your application vendor.

During installation, applications record this information in the following form:

Hkey_Local_Machine\Software\CompanyName\ProductName\Version

The key named Hkey_Local_Machine\Software\Microsoft and its subkey named Windows\CurrentVersion are of particular interest. These subkeys contain information about software that supports services built into Windows 95.

The Setup subkey under Hkey_Local_Machine\Software\Microsoft\Windows \CurrentVersion is used internally by Windows 95 for its Setup program.