Users can later override this option and choose another provider, using the form shown below, in Picture 4. Other search providers are shown with a 2. Given Yahoo's huge number of users, outward referrals are significant. Snap, a directory like Yahoo, also does a similar referral to other search engines at the bottom of its results page. This area shows how search engines get their listings.
Some search engines do it themselves.
For instance, do a search for something popular at Yahoo, and the main results you receive will most likely come from its human-compiled database of listings. You will generally get these at Yahoo only if you search on something more obscure. Unlike Yahoo, some search engines prefer to outsource the listing process. For example, HotBot doesn't index the web itself. Instead, HotBot simply puts its own branding on listings that come from Direct Hit, Inktomi and the Open Directory.