According to a recent article from Information Week, Microsoft's Hyper-V virtualization software will have an advanced "synthetic device" approach to virtual machine I/O, which will address a key virtualization bottleneck.  It is expected to get added to Windows Server 2008 later this year.

When the product finally comes to market, Microsoft hopes it will have a number of features to help distinguish it from the competition. 

Perhaps one of its most distinctive features is the built-in I/O optimization. As virtual machines are stacked up on powerful, multicore hardware, server I/O may get bogged down if several virtual machines experience high I/O demands at the same time. Microsoft has built what it calls "a synthetic device" into Hyper-V. It gets away from its predecessor Virtual Server and Virtual PC products' reliance on device emulation.

With emulation, the hypervisor has to call an emulation program, software that mimics, say, the operations of a network adapter card. The emulation can't run in the same partition as the hypervisor, so overhead was created as the hypervisor told the emulation program what the virtual machine was seeking, and the emulation program took the handed-off instruction and executed it, repeating the process many times. The back and forth "was extremely expensive in performance overhead," said Schutz.

With Hyper-V, a synthetic device that knows how to make use of the native Windows drivers is substituted for the passing of messages between partitions, generating a quicker path to the I/O channel. Under Hyper-V, a virtual machine's access to the hard drive, mouse, video card, network adapter card, or other I/O devices will be managed by a synthetic device that has "driver enlightenment," or knowledge of Windows drivers, not an emulation program, he said.

Find out about other Hyper-V features in this Information Week article.