For example Google’s index, is said to consist of more than three billion pages.
Search algorithm is more sophisticated and third step of a search engine system. Search algorithm is very complicated mechanism that sorts an immense database within a few seconds and produces the results list. The most relevant the search engine sees the webpage the nearer the top of the list. So site owners or webmasters should therefore see site’s relevancy to keywords.
Algorithm is unique for each and every search engine, and is a trade secret, kept hidden from the public.
Most of the modern web search combines the two systems to produce their results | 
