Windows Server 2008 R2, Standard Edition

The Windows Server 2008 R2, Standard Edition is the most common server version of the operating system. Unlike previous versions of Windows Server where basic functions and scalability for memory and processor support was limited to only the Enterprise or
Datacenter Editions of the operating system, Windows Server 2008 R2, Standard Edition is now the default version deployed by organizations. A basic Windows Server 2008 R2 x64-bit Standard Edition system supports up to four x64 professor sockets and 32GB of memory and supports all of the server roles available in Windows Server 2008 R2, with the exception of clustering, cross-file replication (DFS-R technology), and Active Directory Federation Services. The Standard Edition is a good version of the operating system to support domain controllers, utility servers (such as DNS or DHCP), file servers, print servers, media servers, SharePoint servers, and so on. Most organizations, large and small, find the capabilities of the Standard Edition sufficient for most network services.

One of the first things an organization becomes aware of is that Windows Server 2008
R2 ONLY comes in 64-bit (x64 or IA64) versions. 32-bit hardware and a 32-bit installation is no longer supported. The last version of the Windows Server operating system that supported 32-bit is Windows Server 2008.

Source of Information : Sams - Windows Server 2008 R2 Unleashed