http://webhelp.esri.com/arcgisserver/9.3/dotNet/components_of_server.htm
GIS server-- The GIS server hosts your GIS resources, such as maps, globes, and address locators, and exposes them as services to client applications.
The GIS server itself is composed of two distinct parts: the server object manager (SOM) and server object containers (SOCs). As the name implies, the SOM manages the services running on the server. When a client application requests the use of a particular service, it's the SOM that actually provides one for the client to use.
The SOM connects to one or more SOCs. The SOC machines host the services that the SOM manages. Depending on your configuration, you can run the SOM and SOC on different machines and also have multiple SOC machines. The figure above shows a SOM machine connected to two SOC machines
SOC - собственно сам сервис, который и выполняет конечную работу - генерит пользователю картинку, обрабатывает запросы и отсылает ответы.
А авторизация вообще нужна на весь сервер.
