• Spider search engines: Search engines compile their databases using "spiders" or "robots" ("also called bots") to crawl through web space from link to link, identifying and perusing pages.
• Directory engines: In contrast to spider search engines, directories are not automatically generated but are compiled by editors. A website that is submitted to a directory is subsequently catalogued and linked to one ore more topics. As the directories are set up by experienced editors, they generally produce more targeted results.Example is Yahoo.com .
• Hybrid search engines: Many search engines today combine a spider engine with a directory service. The directory normally contains pages that have already been reviewed and accessed.
• FFAL lists (Free For All Link): Free-for-all link lists are pages in which links to website can be entered together with a short comment. Owners of websites thereby enter the registration themselves, and there is no editing board to review the entries, it is free and become immediately effective. Promoting web site to FFAL is not very unpopular because of poor quality directory listings.
• Pay Per Click search engine: A Pay Per Click (also known as Pay Per Ranking, Pay Per Placement or Pay Per Position) search engine enables you to list your site at the top of the search results according to the keyword bid. Example are Overture.com, 7Search.com,FindWhat.com etc.. For more info click here
• Meta: Metasearchers or Metacrawlers do not compile databases. Instead, they search the databases of multiple sets of individual engines simultaneously. Example are Dogpile, MetaCrawler, Mamma etc...
  Note: You don't need to submit your site to metacrawlers as they query other search engines to get results.

How do search engine work:

Search engines compile their databases using "spiders" or "robots" ("also called bots") to crawl through web space from link to link, identifying and perusing pages. Sites with no links to other pages may be missed by spiders altogether. Once the spiders get to a web site, they typically index most of the words on the publicly available pages at the site. It is very important to submit your web pages to all the search engine to get higher ranking. There are lot of automatic submission tools, one of them is Submission2000, it is very powerful and simple to use.

By performing a search using a search engine, you're asking the engine to scan its index of sites and match your keywords and phrases with those in the text of documents within the engine's database.

Spiders regularly return to the web pages they index to look for changes, when changes occur, the index is updated to reflect the new information. However the process of updating can take a while, depending upon how often the spiders visit the web page.

No two search engines are exactly the same in terms of size, speed and content; no two search engines use exactly the same ranking schemes, and not every search engine offers you exactly the same search options. Therefore, your search is going to be different on every engine you use. The difference may not be a lot, but it could be significant. Recent estimates put search engine overlap at approximately 60 percent and unique content at around 40 percent.

Hybrid search engines: In the web's early days, it used to be that a search engine either presented crawler-based results or human-powered listings. Today, it extremely common for both types of results to be presented. Usually, a hybrid search engine will favor one type of listings over another. For example, Yahoo is more likely to present human-powered listings. However, it does also present crawler-based results (as provided by Google), especially for more obscure queries.

Search engine ranking:

In ranking web pages, different search engines follow different set of rules. These may vary from one engine to another. The main purpose of engines, is to return the most relevant pages at the top of their lists. To do this, they look for the location and frequency of keywords and phrases in the web page document and, sometimes, in the HTML META tags. They check out the title field and scan the headers and text near the top of the document. Some of them assess popularity by the number of links that are pointing to sites; the more links, the greater the popularity, i.e., rank of the page.

Some of the Individual search engines are:

• AltaVista
• Excite
• FastSearch
• Google
• Hotbot
• Northern Light