Hyper-V requires a 64-bit system that has Second Level Address Translation (SLAT). SLAT is a feature present in the current generation of 64-bit processors by Intel & AMD. You’ll also need a 64-bit version of Windows 8, and at least 4GB of RAM. Hyper-V does support creation of both 32-bit and 64-bit operating systems in the VMs.
Hyper-V’s dynamic memory allows memory needed by the VM to be allocated and de-allocated dynamically (you specify a minimum and maximum) and share unused memory between VMs. You can run 3 or 4 VMs on a machine that has 4GB of RAM but you will need more RAM for 5 or more VMs. On the other end of the spectrum, you can also create large VMs with 32 processors and 512GB RAM.
As confirmed earlier by Micosoft on their Windows 8 Blog ,after the success of this technology on Windows Server they are finally bringing Hyper-V to Windows 8.Hyper-V was part of previous 2 releases of Windows Server.So Come windows 8 VMWare and Virtual Box will be thing of the past :D