Search Engines versus Search Directories.
Directory provides facility to systematic submission of site. It allows you to submit your website in a specific category. While search engines are such software that do the job of collecting data from all over the web. As far as site submission is concerned, generally, site submission can be of two types, first is to submit a fresh website and other one is to submit those sites that are already submitted, some people do so ,they just resubmit their web site without making significant changes or without indexing any new page .
However, they do not know that all search engines have a good database and if you submit such site that are already available in the search engine’s database, then your site will surely spam.
Directories are not automated programs and generally all the directories are categorized by website experts, while search engines are automated programs, known as robots or spiders.
Directories are basically for browsing purpose however they can be searched while search engines cannot be used as a browser but they use for search purpose.
Directories need human involvement for development and maintenance while search engines have inbuilt programs for any kind of maintenance.
All Search engines use some automated software for indexing the website content and this indexing is done by keywords. While Directories do not have any software to index they just use human efforts.
Some popular directories are yahoo, dmoz etc, and some popular search engines are google, yahoo, msn, AltaVista etc.