Despite the profusion of methods for searching the Web, the most common tools remain search engines and directories. The main difference between search engines and directories is human intervention. Conservative estimates put the current size of the Web at over a billion pages and gauge its growth at a million pages per day. Unfortunately, most search engines don't come close to indexing the whole Net.
Directories rely on human editors to sift through pages and categorizing sites by subject.
Since directories are crafted by hand, they are less comprehensive than search engines. The largest directory, called The Open Directory , is tiny compared to search engines. It's current index is only about two million sites. Top Search Sites Directories and search engines have different virtues, so most major search sites meld aspects of each. AltaVista, for example, supplements its search engine with a directory that uses listings from the LookSmart and Open Directory indexes.