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VMMs Versus Hypervisors

Tuesday, 11 July 2006 by Michel Roth

The Virtual PC Guy tries to explain the differences between VMMs and Hypervisors: Today I would like to try and clear up some confusion that seems to be out there at the moment. People have been throwing around the terms 'VMM' and 'hypervisor' recently - and it is fairly apparent that the vast majority of the general populace does not know clearly what these terms mean, and specifically what the key differences are between the two.

So let us start with the first one - 'VMM'.

This term suffers from the problem that there are actually two meanings for 'VMM'. The first is 'virtual memory manager' - this is part of the Windows operating system and has nothing to do with computer virtualization - and everything to do with operating system memory management. This is not what I am discussing today :-)

The second meaning is 'Virtual Machine Manager'. There are a number of different programs and implementations that use the moniker 'Virtual Machine Manager'. In the simplest terms - the VMM is the piece of software responsible for monitoring and enforcing policy on the virtual machines for which it is responsible. This means that the VMM keeps track of everything happening inside of a virtual machine, and when necessary provides resources, redirects the virtual machine to resources, or denies access to resources (different implementations of VMMs provide or redirect resources to varying levels - but that is a topic of discussion for another day).

Read on here.