Kinds of search engines

There are two main kinds of search engine: pure and meta.

 

In more detail, the two main kinds of search engines are:

1. Pure, which have their own databases, i.e., their own index of links to web pages. They come in two varieties: spider databases and directories.
2. Meta-search engines, which do not have their own databases. They combine the databases from several pure search engines.

Spider databases send "software spiders" across the web searching for new pages. The spiders crawl from links in the database onto the pages themselves. 

Spiders crawl the web daily to get the very latest pages. Google, Yahoo and MSN have the most important spider databases. But there are several others, including: AltaVista and Alltheweb. Of all the spider databases, Google is by far the most successful. 

Directories have been somewhat over-shadowed by the success of spider databases. They do not use spiders to find links, and rely on humans to provide entries. This means they provide fewer strange results, but are much smaller in size. Humans are less efficient and motivated than the remorseless, hungry spiders. Better directories include Yahoo Directory and Overture.

In recent times, the meta search engines have become much less popular than the raw spider databases. But the better ones should have a place in any aspiring web masters' daily routine. After all, they have the potential to deliver as many results as the big three put together. Better ones include Mamma and Dogpile.