The Internet was reaching a vast population of non-technical users who were often unable to use advanced querying techniques to reach the information they were seeking and the sheer volume and complexity of the indexed data was vastly different from that of the early days. Combined with increases in processing power, search engines have begun to develop different sortys of algorithms.
A complex mathematical formula used by a search engine to rank the webpages that it finds by crawling the Web is termed as ranking algorithms. Google was the first of its kind started by two PhD students at Stanford University, Sergey Brin and Larry Page.
Every search engine (Google, Yahoo, Microsoft and Ask.com) has its own relevancy algorithm (rules for ranking), which is continuously developing as search engines are learning from their experience. The search engines' algorithms are very top secret. There are many people working outside the search engine industry to attempt to reverse engineer the code in order to understand their working in an attempt to help people to rank higher in the results. No search engine reveals exactly how its own algorithm works to protect itself from competitors and those who wish to spam the search engine.
As a search engine may use hundreds of factors in ranking the listings on its SERPs; the factors themselves and the weight each carries can change continually, and algorithms can differ widely, with a web page that ranks #1 in a particular search engine possibly ranking #200 in another search engine, or even on the same search engine a few days later.
Some sites focus on exchanging, buying, and selling links, often on a massive scale. This has spawned an online industry, that survives to this day, focused upon selling links designed to improve PageRank and link popularity, and not to drive human site visitors, with links from higher PageRank pages selling for the most money.
Signals influencing a page's rankings include:
1.Keywords in the title tag.
2.Keywords in links pointing to the page.
3.Keywords appearing in visible text.
4. Link popularity (PageRank for Google) of the page.