Difference between the architectures of SSPs and SharePoint Service Application

Referred URL  - http://manojvnair.blogspot.in/2011/04/difference-between-architectures-of.html

SharePoint 2010 has some new features and components, which help to overcome difficulties such as redundancy and service-sharing that we faced while using SharePoint 2007.
Services in MOSS 2007 were implemented with the help of Shared Service Providers or SSPs. But we cannot use the services of one SSP for another SSP. So each SSP has to have its own set of services and applications, which increases redundant data in the farm.

For example, different managers in the same organization use a SharePoint site to maintain official data associated with an SSP. This SSP is associated with different services, such as Search service, BDC service, and a user profile service. A project manager in this organization requests an exclusive user profile service to maintain project data security. To provide this, we first need to create a separate SSP for the project manager and then a separate service called user profile service - project name. Next, we need to associate the SSP with the service and configure the user profiles service for the manager. However, when we do this, the project manager will not be able to access the Search service and BDC service. So you need to associate the Search service and the BDC service for this SSP as well.
If there are numerous similar requests, then it will lead to data redundancy.

SharePoint 2007 architecture

In SharePoint 2010, this redundancy and service-sharing issue is resolved because SSPs are replaced by Shared Service Applications or SSAs. Commonly known as service applications, SSAs allow services to be shared across farms and web applications.
Suppose that the organization that uses SharePoint 2007 for maintaining department data were to upgrade to SharePoint 2010. SharePoint 2010 would contain a web application, WebApplication1, connected to a User Profile and services such as Search service and BDC service. The project manager's request for an exclusive user profile service would now be implemented differently.
We would create a web application, WebApplication2, and provide a user profile service application exclusively for this web application. Then, you would be able to associate the web application with all service applications shared across the web application. So the project manager would be able to access the other service applications in addition to using the new service application, which eliminates the scaling issues that exist with SSPs. 

SharePoint 2010 Architecture

Besides these differences in their ability to share services, the architectures of SSP and SSA have many other differences, as listed in the "Differences between the SSA and SSP architectures table"