The many search engines of the Internet, more specifically, the
World Wide Web use software programs called spiders, wanderers or
'bots, (robots), to gather information frome web sites, (by "crawling"
them.) Then they index this information for searching. The meta
information and indexing can take up huge amounts of computer memory.
(Both storage and active memory.) The methods by which they index
and the algorithms by which they retrieve and rank data can be different.
As a result, different engines can produce somewhat different results.
When looking for things of importance, it's usually wise to use
at least a few different engines.
Teoma: New, and maybe Improved Search Algorthms
Google: Well known, pehaps overexplosed. Great product, but give Teoma a shot as well.