Appendix B. Introduction to WMI

The Windows Management Instrumentation (WMI) API was developed by Microsoft in 1998 in response to developers' and system administrators' ever growing need for a common, scriptable API to manage the components of the Windows operating system. Before WMI, if you wanted to manage some component of the operating system, you had to resort to using one of the component-specific Win32 APIs, such as the Registry API or the Event Log API. Each API typically had its own implementation quirks and required way too much work to do simple tasks. The other big problem with the Win32 APIs was that scripting languages, such as VBScript, could not access them. This limited how much an inexperienced programmer or system administrator could programmatically manage systems. WMI changes all this by providing a single API that can be used to query and manage the Event Log, the Registry, system processes, the file system, and almost any other operating system component.

The WMI architecture relies heavily upon the concept of providers. These providers gather and supply information to the underlying objects being queried. Depending on the WMI information you are trying to retrieve, WMI will contact the specific provider that can retrieve the information (e.g., SNMP or the Registry).

WMI is installed as part of the following operating systems: Windows 2000 Professional, Windows 2000 Server, Windows XP, and Windows 2003 server. WMI is available as an installable option on Windows 98 and is included as part of service pack 4 for Windows NT 4.0 systems. If you are going to use WMI on these older operating systems, I suggest you download the latest version of the WMI client from MSDN (http://msdn.microsoft.com/).

The learning curve to develop WMI scripts is relatively short if you have any experience with a scripting language. In fact, once you understand how to reference, enumerate, and query objects of a particular class with WMI, it is straightforward to adapt the code to work with any managed component, including DNS. And fortunately, by understanding just a few guidelines, you can convert VBScript code to Perl and vice versa.