Why it is not replaced by COM, how it works, network DDE, links to other sources of information. DDE is support is being removed from Windows (Windows 7 x64 seems to have an issue with it)
"Only one third of a search engine is devoted to fulfilling search requests. The other two thirds are divided between crawling (sending a host of single-minded digital organisms out to gather information) and indexing (building data structures from the results)." By George Dyson