windows server 2008 and 2008 r2 system requirements

Minimum hardware requirement for installing Windows Server 2008 R2, 

For server 2008

Processor: Minimum 1 GHz (IA-32) 1.4 GHz (x86-64 or Itanium) and Recommended 2 GHz or faster

Memory:    Minimum 512 and recommended 2 GB greater

Hard drive: for 32-Bit 20 GB and 64-Bit 32 GB recommended 40 GB greater

for Server 2008 R2

Processor: Minimum 1.4 GHz (x86-64 or Itanium) and Recommended 2 GHz or faster greater

Memory:   Minimum 512 and recommended 2 GB  greater

Hard drive: Minimum 32 GB and recommended 32 GB and greater