Google, Yahoo and others use several activities to deliver the results you see on your desktop:
– They use `spiders` or `crawlers` also referred in Google terms as a `Googlebot` which are software to fetch the data from web pages.
– They `index` the website by using the `spiders` or `crawlers` and then store this information in a digital bank, filing everything in specific areas so they can use these pages when you type in a search phrase.
– Search engines then use a process where it compares the search string in the search phrase and looks to find what page is most relevant from its database (Its digital bank)
– The search engine then needs to the calculate the relevancy of the pages it has identified, it will notice how many of the words from the search string are used and where they are placed on the website
– It will then retrieve your search results, it will basically make its decision about what is most relevant and then display the results on your PC browser.
The algorithms that the search engines uses are updated dozens of times per month, when you see changes in Google or Yahoo results this is down to a change in the mathematical equation used to determine web results.
The main part of the algorithms will always remain the same yet the smallest change can result in major changes in the results you see.