Windows Server 2008 Maximum memory limit:
Windows Server 2008 x86 Windows Server 2008 Standard Edition, supports maximum 4GB memory Windows Server 2008 Enterprise Edition, supports maximum 64GB memory Windows Server 2008 Datacenter Edition, supports maximum 64GB memory
Windows Server 2008 x64 with or without Hyper-V role Enable Windows Server 2008 Standard Edition, supports maximum 32GB memory Windows Server 2008 Enterprise Edition, supports maximum 1TB memory Windows Server 2008 Datacenter Edition, supports maximum 1TB memory
Windows Server2008 R2 maximum memory limit:
Windows Server 2008 R2 with Hyper-V role Enable Windows Server 2008 R2 Standard Edition, maximum support 32GB memory Windows Server 2008 R2 Enterprise Edition, maximum support 1TB memory Windows Server 2008 R2 Datacenter Edition, maximum support 1TB memory
Windows Server 2008 R2 without Hyper-V role Enable Windows Server 2008 R2 Standard Edition, maximum support 32GB memory Windows Server 2008 R2 Enterprise Edition, maximum support 2TB memory Windows Server 2008 R2 Datacenter Edition, maximum support 2TB memory
The information from the above collation is from: WINDOWS SERVER 2008/2008 R2 MAX MEMORY