Common Principles search engine
   To understand SEO you should be aware of the architecture of search engines. They all contain the following main components:

   Spider - a browser-like program that dismisses web pages.

   Crawler - a program that automatically follows all links on any web page.

   Indexer - a program that analyzes web pages downloaded by the spider and crawler.

   Database-storage for downloaded and processed pages.

   Results engine - Search Results extracts from the database.

   Web server - a server that is responsible for interaction between the user and other search engine components.

   Implementation of specific search mechanisms may differ. For example, + Spider Crawler + Indexer component group might be implemented as a single program that downloads web pages, analyzes them and then uses their links to find new sources. However, the components listed are inherent to all search engines and SEO principles are the same.

   Spider. This website program downloads as a web browser. The difference is that a browser displays the information presented on each page (text, graphics, etc.) while a spider does not have any visual components and works directly with the underlying HTML code of the page. You may know that there is a standard Web browser option to view HTML source code.

   Crawler. This program finds all links on each page. Its task is to determine where the spider should go either praising or alloys based on a predefined list of addresses. Crawler follows these links and tries to find documents not already known to the search engine.

   Indexer. This component parses each page and analyzes the various elements, such as text, headers, structural or stylistic features, special HTML tags, etc.

   Database. This is the storage area for data search engine downloads and analyzes. Sometimes it is called search engine index.

   Engine results. Engine results page rank. It determines which pages best match the user's request and in a way that sites should be listed. This is done in accordance with the search engine ranking algorithms. It follows that page rank is valid and interesting property and any SEO specialist is most interested in, when trying to improve his site search results. In this article, we will discuss the factors that affect SEO on site in some detail.

   Web server. Search engine web server usually contains a HTML page with an input field where the user can specify the search query he or she is interested in web server is also responsible for displaying search results to the user in the form of an HTML page.