end of the line, and lower capital costs, higher asset utilization, and lower availability at the other end. Virtualization can enhance availability.

GUSTAV You will tend to use the VM, because while there are differences now at the hypervisor level, those differences are converging relatively rapidly and will ultimately disappear.

If you’re worried about the long-term trend of hypervisors, you’re worried about the wrong thing. Choose the VM that is most compatible today to the application you are going to run. If you’re doing desktop virtualization, you’re probably going to use CXD (Citrix Xen Desktop). If you’re doing Windows server virtualization, you’re going to use either Veridian or, depending on what you’re trying to do regarding availability management, VMware.

The first question to ask is, “What are you used to?” That’s going to determine what your likely VM is. The second question is, “What is the problem you’re trying to solve?” The more complex the management problem, the more attractive an integrated tool suite from VMware becomes. If you are saying, “I don’t have complex problems now but I’m going to have complex problems in three or four years,” the more attractive Microsoft becomes. If you are going to build it on your own and/or have your own toolsets to integrate, which is most of the enterprise, you’re going to find the Xen/Citrix option more attractive. If you’re coming from the desktop side, you’re at the other side of Citrix, and that is back to Xen. Where you’re coming from is going to determine your VM product selection much more than where you’re going, because they’re all heading to the same place. CROSBY Both Microsoft Hyper-V/System Center and VMware VSX and VC are complete architectures. Neither of them has a well-established ISV (independent software vendor) ecosystem significantly limiting customer choices. That said, I think the ecosystem around VMware is now starting to emerge as a result of the adoption of standards-based APIs.

What worries me is whether the missing functionality in any vendor’s product needs to be developed by the vendor or whether the customer is OK with a solution composed of a vendor product and ISV add-ons. Both Stratus and Marathon offer fault-tolerant virtual machine infrastructure products using Citrix XenServer as an embedded component. That’s because they focus on how to build the world’s best fault tolerance, whereas Citrix, VMware, and Microsoft do not. We have an open architecture, and that allows the world’s best talent to look at how to extend it and build solutions beyond our core competence. This is a very powerful model.

From an architectural perspective, I am absolutely passionate that virtualization should be open because then you get this very powerful model of innovation.

I have an ongoing discussion with one of the major analyst organizations because virtualization in their brains is shaped like VMware’s products are shaped today. They think of it as ESX Server. If VMware’s ESX Server is viewed as a fully integrated car, then Xen should be viewed as a single engine. I would assert that because we don’t know where virtualization is going to be in five years, you do not want to bind your consumption of virtualization to a particular car right now. As technology innovation occurs, virtualization will take different shapes. For example, the storage industry is innovating rapidly in virtualization, and VMware cannot take advantage of it with its (current) closed architecture. Xen is open and can adapt. It runs on a 4,096-CPU supercom-puter from SGI, and it runs on a PC. That is an engine story; it is not a car story.

It’s really critical that we have an architecture that allows independent innovation around the components of virtualization. Virtualization is just a technology for forcing separation as far down the stack as you can—on the server, separated by the hypervisor, in the storage system—and then let’s see how things build. I’m not in favor of any architecture that precludes innovation from a huge ecosystem. HERROD I actually agree on several parts. Especially for the middle market, the number-one thing that people need is something easy to use. I think there’s a reasonable middle road that can provide a very nice framework or a common way of doing things, but also have tie-in to the partner ecosystem. Microsoft has done this very well for a long time. BOURNE These bindings may be ABIs (application binary interfaces) or they may not be, but they sound like the analogue of the ABIs. ABIs are a pain in the neck. So are these bindings a pain in the neck? CROSBY Bindings are a very hot area. The hottest one for us right now is that the VM you run on XenServer will run on Microsoft Hyper-V. This is a virtual hardware interface, where, when you move a virtual machine from one product to the other, the VM will still think it has the same hardware underneath it.

If you take a VM from VMware and try to run it on Citrix, you will get a blue screen. It’s just the same as if you took a hard disk out of a server and put it in another server and expected the operating system to boot cor-