Difference Between Windows server 2008 and R2

 Windows 2008 Server,

Windows Server 2008 (Win2k8) is one of Microsoft Windows' server line of operating systems. Released to manufacturing on February 4, 2008, and officially released on February 27, 2008, it is the successor to Windows Server 2003, released nearly five years earlier.

Windows Server 2008 is built from the same code base as Windows Vista; therefore, it shares much of the same architecture and functionality.

Whats in Windows Server 2008 :
Virtualisation:
Server Core
IIS
Role Based Installation
RODC
NAP
Bit Locker
Powershell
Fail-over Clustering
Self Healing NTFS
System Resource Manager

Windows Server 2008 R2,

Windows Server 2008 R2 is a server operating system produced by Microsoft. It was released to manufacturing on July 22, 2009 and launched on October 22, 2009. According to the Windows Server Team blog, the retail availability was September 14, 2009.[4] It is built on Windows NT 6.1, the same kernel used with the client-oriented Windows 7. It is the first 64-bit-only operating system release from Microsoft.

Whats New in Windows Server 2008 R2:
64-Bit Only
Support for 256 cores
Core Parking
Remote Desktop Services
New Hyper-V
Live Migration
Support .NET Frameworks in Server Core
Powershell 2.0
Remote Server Management
Active Directory Administrative Center