The Solid ICE approach lets users add an application to their desktops, then captures the addition and saves it as a virtual machine image specific to a given user. A policy engine tracks what's on each user's desktop and enforces restrictions on what can be added, Clark says.
In addition, Qumranet sought to make the desktops virtualized on central servers as efficient as possible. "We said, 'let's make a big impediment to desktop virtualization go away. Let's put the hypervisor into the operating system,' " said Clark. With an open source hypervisor in Linux, virtual machines may be created to run either Windows or Linux above the kernel's KVM.
To round out its desktop product, however, it needed to invent a new and proprietary protocol that it calls Spice. Spice gives Solid ICE a way to manage connections between virtualization servers and desktops, claims Clark.
Microsoft's Viridian, to be launched within six months of the February launch of Windows Server 2008, also will be a hypervisor built into the operating system. It will run Microsoft's Virtual Server virtual machines, with an ability to convert VMware's virtual machines into Viridian-compatible VMs.
VMware's ESX Server also can run either Windows or Linux operating systems above the hypervisor. It's positioned as an independent layer of virtualization software outside either the Linux or Windows any operating system.