Windows Server 2008 builds on the success and strengths of its Windows Server predecessors while delivering valuable new functionality and powerful improvements to the base operating system. New Web tools, virtualization technologies, security enhancements, and management utilities help save time, reduce costs, and provide a solid foundation for your information technology (IT) infrastructure. A Windows Server User CAL permits one user (using any device) to access or use the server software. User CALs are likely to be more cost effective than Device CALs if there are multiple devices per user (for example, a user has a laptop and handheld computer accessing Windows Server) Software Assurance (SA) is Microsoft's maintenance program that provides product support, software upgrades, and more.