[B]What is the difference between index and cache?
If anyone the answer please explain me…[/B]
Cache
when search engine bot or crawler come to your page or found any update on site
Indexing
After reading the updated element it stores those new elements in Search Engine’s database. This restoration process referred as Indexing.
I’ve worked with search engines for a bit, having written one myself, so I’ll wade in.
When Google’s crawlers come onto your web page it will take a snapshot/copy of your page as it sees it. It will use this snapshot to obtain information about your website, and will replace this when it visits your site next and finds a reason to update its records. This copy is stored within its cache and is referred to as a cached version of your page. When you click the cache button underneath a Google result, Google will show you the cached version of that page and when its crawlers obtained it.
Once the bot has grabbed a copy of your page it will break it down within its own data structure in order to map different search results to different web pages (a primitive example of this is an Inverted Index). This broken-down information is referred to as Google’s index. From an outside view it is similar to a database, but the index is effectively a gigantic map of values, locations and weightings from web pages (e.g. all the words in a web page, along with their character location in the cached document). In a basic search engine you can map words and then provide search results from your inverted index based on occurrences of words and their position within the document. Naturally, Google is far more complex than this, so it’s safe to assume that their index is far more complex than an inverted index.
If you’re interested in the innards of Google back when it was a research project you may be interested in this.