Yahoo search uses bing (that's right Microsoft bing) while alta vista uses the original yahoo search engine.
AltaVista is a web search engine owned by Yahoo.
Yahoo!'s Database
Besides Yahoo, there are Google, Bing, AltaVista, DogPile, and many others.
Yahoo answers questions
There is a big difference. Yahoo is a search Engine.Twitter is a social network.
There are several sites, such as Google, Altavista, Yahoo, and many others more.
Yahoo, Google, Ask, Bing, Duck Duck Go, Baidu, Cuil, Lycos, AltaVista, and Excite.
Webcrawler
I'll give you more than two: Yahoo!, Google, Altavista, Dogpile, Bing, Cuil, and Lycos.
In fact there is no main difference between them , just we have in interface
yahho is a website explorer is a web broser
AltaVista was created in 1995.