PAGE CACHING
Google takes a snapshot of each page it examines and caches (stores) that version as a back-up. The cached version is what Google uses to judge if a page is a good match for your query. Practically every search result includes a Cached link. Clicking on that link takes you to the Google cached version of that web page, instead of the current version of the page. This is useful if the original page is unavailable because of:
• Internet congestion
• A down, overloaded, or just slow website
• The owner's recently removing the page from the Web
Sometimes you can access the cached version from a site that otherwise require registration or a subscription. Since Google's servers are typically faster than many web servers, you can often access a page's cached version faster than the page itself. If Google returns a link to a page that appears to have little to do with your query, or if you can't find the information you're seeking on the current version of the page, take a look at the cached version.

PAGERANK
PageRank (PR) relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important”. Important, high-quality sites receive a higher PageRank, which Google remembers each time it conducts a search. Of course, important pages mean nothing to you if they don't match your query. So, Google combines PageRank with sophisticated text-matching techniques to find pages that are both important and relevant to your search. Google goes far beyond the number of times a term appears on a page and examines all aspects of the page's content (and the content of the pages linking to it) to determine if it's a good match for your query.