Difference between Discovery service AND Organization service

Discovery Service : The Discovery service web service is used to determines the organizations that a user is a member of, and the endpoint address URL to access the OrganisationService Web service for each of those organizations this discovery service is necessary because Microsoft Dynamics CRM is a multi-tenant environment a single Microsoft Dynamics CRM can host multiple business organizations. By using the discovery web service, your application can determine the endpoint address URL to access the target organisation’s business data. Organization Service : It is a primary web service that accesses data and metadata of an organization. This web service contains the methods that you use to write code that uses all the data and metadata in Microsoft Dynamics CRM.