Here's the basic question: where does the hypervisor--the software layer that underpins server virtualization--live and who owns it? Is it just part of the server or is it just part of the operating system?
For now, to be sure, it's often something that IT shops purchase from a third-party--we're mostly talking from VMware here. However, pretty much everyone expects that over time this foundational component will be increasingly built-in--even if the higher-level value-add management and virtualization services that make use of it are explicitly purchased from a variety of sources.
Virtualization vendors have often considered this an important question.
A few years back, I had written a piece about how Novell and Red Hat were adding the Xen hypervisor to their Linux distributions. And that Microsoft had made clear its intention to add virtualization to Windows--technology now known as Hyper-V. In short, virtualization was starting to move into the operating systems of a number of vendors.
Well, that notion didn't sit well with Diane Greene--then CEO of VMware--as she made clear to me by coming over and grabbing me by the lapels(only somewhat figuratively) at an Intel Developers Forum event. From Diane's, admittedly biased, perspective the hypervisor should be independent of any single operating system. I hadn't said otherwise. But I apparently didn't make the opposing case enthusiastically enough.
At the time, VMware ESX Server (its native hypervisor) had to be installed as with any other third-party software product. However, over time, VMware and other virtualization vendors came out with versions of their products that could be installed from a USB memory stick or other form of flash memory. It was called ESXi in VMware's case.
Thus the embedded, or at least embeddable, hypervisor was born with rumors throughout 2007 becoming product announcements in September of that year.
There's actually a lot to be said for the embedded hypervisor. Lots of IT environments--especially enterprise ones--do indeed have a mix of operating systems and operating system versions. Given that, there is indeed a lot to be said for the idea that hypervisors just come with the server as a sort of superset to the firmaware, like BIOS, already loaded on every system. Then IT administrators could just configure any guest OSs they want on top.
It's logical. But it's not really playing out that way--at least so far.
After all the initial excitement in late 2007, embedded hypervisors didn't really go anywhere in 2008. Instead, Microsoft's Hyper-V rolled out and KVM found its way into the main Linux kernel as an alternative style of Linux virtualization backed by Red Hat.
Whether or not it makes "sense," in some theoretical, architectural sense, it's no longer clear to me that embedded hypervisors are going to be the path that the industry predominantly follows.
Rather, at the moment, homogeneous environments are tending towards whatever is built into the OS. And enterprises are going to their ISV of choice--sometimes Citrix for XenServer--but far more often VMware for ESX.
At the very least, it now looks as if--for the foreseeable future--IT shops will acquire virtualization, including hypervisors, in a variety of ways that vary as a function of their individual requirements, circumstances, and vendor alignments.