Subject Directories are reviewed and arranged into subjects by people rather than by a computer. Websites are placed into categories and may be reviewed or summarized. Subject directories include a smaller section of web sites and generally search broad, general topics.
Search Engines use robots or "spiders" to crawl the Web to find sites to put in an index. Though search engines have similar parts, they don't all find the same things. Try using more than one.
Need help creating a better search? Check out these Search Tips.