Encyclopedias, dictionaries and other reference works are a good place to begin if you do not already know much about a topic or need a short overview.
Writers look to reference works for general information and factual evidence.
For example, using Britannica Online, on the left, and entering "Alfred Hitchcock" in the search box, this is one item from the results.
radio; early radio
For instance, using Credo Reference (on the left) and entering "early radio", these are the search results.