Whenever an item is entered into a search engine, a list of results concerning the item being queried is delivered. Users generally tend to visit websites which are near the top of the list because they are perceived as being more relevant. Why some websites achieve better results than others is because of a powerful technique of marketing known as Search Engine Optimisation (SEO). The technique helps to deliver more traffic from search engines because it enables a particular website to achieve a higher rank than hundreds of similar websites.
How search engines operate
The first thing to be learned about SEO is that search engines are not human beings, and there are plenty of differences between how human beings and search engines regard web pages. Unlike human beings, search engines operate on text and despite the rapid advances in technology, search engines are not intelligent enough to appreciate good design or enjoy the music and sound. Instead, they crawl the web looking at the text on a particular website to gather information on what the site is all about. This is a basic explanation, though search engines perform other activities to deliver search results, such as indexing, processing and calculating relevance
In the first place, the search engines crawl the web to see what is available. They use a piece of software known as a spider or a crawler which follow links from one page to another and index everything that they find during their search. There are well over 20 billion pages on the web and it is often impossible for a spider to visit every site on a daily basis to check for the appearance of new pages or the modification of existing ones. This is why sites are often visited every month or two.
When a search request is entered into a search engine, the engine compares the string with the indexed pages on the database and being likely to find many pages, the relevancy of each page is calculated. Different algorithms are used to calculate relevancy and each algorithm uses different weightage for factors such as keyword density and meta tags. This is part of the reason for the difference in search results on different search engines. It is common knowledge that all the major search engines periodically modify their algorithms and this is one reason why so much effort is devoted to SEO to enable web pages to be modified as necessary.
Though the basic principles of the way search engines operate are similar, the differences leads to major changes in the rele, for instance, vancy of the results and even SEO experts find it difficult to stay on top in order to optimise properly. For instance, Yahoo! and Bing, the greater importance to on page keyword factors while Google gives more importance to links.