What are the major feature based differences between Windows Server 2008 & Server 2008 R2?

Server2008 is based on the vista kernal whereas Server2008 R2 is based on the Windows7 kernal

Server2008 R2 has64 bit processor designed to support upto256 logical processors and better management of memory

• WS2008R2 is available only on62bit platform where WS2008 is available in both32 and63bit
• WS2008 is based on Windows Kernal V6.0 (Same as Windows Vista) and WS2008R2 based on Windows Kernal V6.1 (Same as Windows7)
• WS2008R2 is a latest version of IIS which is IIS7.5 (now IIS8 and8.5 released with WS2012 and WS2012R2 respectively)
• PowerShell2.0 was introduced with WS2008R2