Comparison of results between engines, given the same keyword search, yield quite different findings based on search capabilities, size, and updating frequency. These meta engines are very fast but they do not offer the same level of control over the relationship between keywords as do individual search engines. They can be used as good starting points to compare sites across several databases at once. Recently, the capabilities of meta-tools have been improved to include such useful features as the ability to sort results by site, by type of resource, or by domain, the ability to select which search engines to include, and the ability to modify results. These modifications have greatly increased the effectiveness and utility of the meta-tools.
Subject directories are lists compiled by people.
They are organized in a hierarchy where each subject includes a list of sub-topics. In other words, the best sites on a topic are not necessarily listed first. Sites are compiled through submission of URLs by site creators and human selection. One advantage of subject indexes is their browsability, although this feature is only suitable with fairly general topics. There are various ways to begin a Web search.