Search Engine Classifications

There are different classifications of search engines, namely:

• Crawler-based (traditional, common) search engines
• Directories (mostly human-edited catalogs)
• Hybrid engines (META engines and those using other engines' results)

Crawler-based search engines, e.g. Google, Yahoo & Bing, are those that use programs called spiders who crawl web pages to gather information that are sent back to their respective servers for storage and future indexing.

Directories such as www.DMOZ.org, a.k.a Open Directory Project or ODP (DMOZ stands for "Directory.Mozilla"), and Yahoo! Directory are considered "human powered" search engines. DMOZ is constructed and maintained by a community of volunteer editors. It costs $299 to submit to Yahoo! Directory for an annual review ( $600 for adult sites) and you can be listed for just a few days while submitting for free gives you no guarantee of getting listed at all.

Meta search engines such as Dogpile and Clusty gets their data from multiple search engines like Google and Yahoo! and then serve them in a search results page for every query or search you make.

I hope these information will help you more with your Search Engine Optimization (SEO).