There are a ton of new improvements for Hyper-V with the preview release of Server 2012 R2. Microsoft has been running an excellent
blog series all about the new features of Server 2012 R2, and if you have some - or a lot - of free time, the posts are definitely worth a look. Additionally, Microsoft has released a free
ebook for the Server 2012 R2 preview.
One of my favorite improvements in the Hyper-V realm is the introduction of version 2 virtual machines. Up until now all virtual machines in Hyper-V had the same set of legacy virtualized hardware. This was necessary from Microsoft's perspective to support the maximum number of potential OSes. Because they were trying to support everything from Windows NT to Server 2012, they had to pick some truly archaic hardware. This included an AMI BIOS, Intel 440BX chipset motherboard, S3 Trio graphics display adapter, and an Intel/DEC 21140 network adapter. The virtualized hardware did not support boot from SCSI, so the main VHD for the system had to be on an IDE bus. PXE boot was slow at best, as was a network install of the OS. It's true that virtualizing hardware can speed it up, but MS had done all that they could and now found themselves with several performance bottlenecks. The solution? Get rid of all that legacy virtualized hardware.
Version 2 of the virtual machine boots from a UEFI firmware supporting Secure Boot instead of the legacy BIOS. The only controller available is SCSI for both hard drives and CDROM. The keyboard, mouse, and video are all using software-based drivers and do not require using emulated hardware, which reduces resource usage. Several other legacy devices have either been replaced with software or removed completely, as they are not needed by a modern OS. The net result is a virtual machine that is aware of the fact it is virtualized and runs more efficiently with less resources than its predecessor.
The main caveat of version 2 is that it requires the guest OS to be the 64-bit version of either Windows 8 or Server 2012. No other OSes are currently supported. So moving forward, you should be able to use version 2 for all your new VMs, but your legacy VMs will have to stay at version 1. That's not to say that there won't be extended support for other OSes in the future, but for the moment MS is hoping you'll take the bait and jump on the Win8/2012 train. With 8.1 and 2012 R2 around the corner, it's probably time for even the more conservative companies to start adopting the next generation. Microsoft
announced just a few days ago that both 8.1 and R2 will be released on October 18th. If you are looking to dip your toe in the Hyper-V scene, now would be an ideal time.