Type 1 and Type 2 Hypervisors Explained

Type 1 and Type 2 Hypervisors Explained

In a recent discussion, the topic of Type 1 and Type 2 hypervisors came up. To some, this is an arbitrary distinction that doesn't matter much as there's already an inherent understanding of what the requirements are for a virtualization solution.

Simply put, the distinction between Type 1 and Type 2 has to do with whether an underlying operating system is present.Virtualization Revieweditor Keith Ward touched on part of this topic in apost about KVM virtualization in regards to Red Hat.

I'm convinced there's no formal standards-based definition of Type 1 and Type 2 criteria. However, I did likethis very succinct piece of literature from IBM. While it doesn't have an exhaustive list of hypervisors and their types, it does give good definitions. The material describes a Type 1 hypervisor as running directly on the hardware with VM resources provided by the hypervisor. The IBM Systems Software Information Center material further states that a Type 2 hypervisor runs on a host operating system to provide virtualization services.

Some are obvious, such as VMware ESXi and Citrix XenServer being Type 1 hypervisors. My beloved Sun VirtualBox, VMware Server and Microsoft Virtual PC are all Type 2 hypervisors.

With that said, it's unclear where Hyper-V fits into the mix. Information likethis Microsoft virtualization team blog post pull Hyper-V closer to the Windows Server 2008 base product.

The relevance of Type 1 and Type 2 distinction is academic, in my opinion, but something I wanted to share here. Your thoughts?Drop me a note or share a comment below.

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