Hardware Requirements for Windows Server 2008
Before you arrange and use Active Directory, you need to install the operating system Windows Server 2008. Start by making certain the hardware you plan to use as domain controllers is able to run the operating system. This list shows you the minimum and recommended hardware levels for Windows Server 2008:
Processor 1 GHz (x86 CPU) or 1.4 GHz (x64 CPU)
Memory 512MB required; 2GB or higher recommended.
Hard Disk 10 GB required. 40 GB or more recommended.
Video Super VGA or higher video card and monitor.
Hardware Must be on the Windows 2008 Hardware Compatibility List.