In Windows Server 2008 and Windows Server 2008 R2 assigning memory to virtual machines is a static process. When you assign 4 GB to a virtual machine it uses these 4 GB, no more, no less. When not all of this memory is used than it’s bad luck. Once assigned it cannot be used for other purposes. So, when you have a Hyper-V host with 32GB of memory, you can create 15 virtual machines each configured with 2 GB of memory. The last 2 GB will be used by the parent partition itself.

New in Windows Server 2008 R2 SP1 is a feature called “Dynamic Memory”. This feature can assign more memory to a virtual machine (while running) when the virtual machine needs more memory. It can also remove memory from the virtual machine when this memory can be used for other virtual machines.

Some people think VMware’s and Microsoft’s approaches to dynamic memory is exactly the same. In this article I explain both the similarities and the differences. Read More….