Windows Server 2008 R2, or simply “R2” for short, is the second release of Windows
Server 2008. It isn’t a completely new release, but rather adds additional features and
refinements to the existing release.
Release Cadence
Beginning with Windows Server 2003, Microsoft moved to a server release cycle that
was designed to have a major release every three to five years (Windows Server 2003,
Windows Server 2008), with a minor release at the approximate midpoint of the major
release cycle (Windows Server 2003 R2, Windows Server 2008 R2). This change allowed
Microsoft to move away from including new functionality in service packs (SPs), while
providing customers with a more stable and predictable server environment.
An R2 release is more than an SP, but less than a full major release. Windows Server
2008 R2 includes Windows Server 2008 SP2, but it also adds many new features and
functionality that were not part of Windows Server 2008