Start with MSDN under http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wmisdk/wmi/wmi_start_page.asp
WMI is not really "code of its own", it's more an interface to the internal system manage,ment components of Windows. Information can be exchages with the interface by way of the WQL query language or via e.g. direct COM calls as WMI is COMable.
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There are two types of vessels, submarines and targets.
