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A client-based virtual machine is an instance of an operating system that is managed centrally on a server and executed locally on a client device. Although the operating system disk image is updated and backed up by synchronizing regularly with a server, a constant network connection is not necessary for a client-based virtual machine to function.
A client-based virtual machine can run without a host operating system directly on a type 1 (or bare-metal) hypervisor, or at the same time as a host operating system, utilizing a type 2 hypervisor. The hypervisor provides an interface to the local hardware, taking the place of drivers that would normally be contained in an operating system image. This allows virtual machine images to be standardized and usable across a large variety of different hardware configurations.
However, in order to enable more advanced functionality, virtual machines must often reach through the hypervisor and interact with the local host hardware directly. This requires the virtual machine to have specific drivers for the hardware on which it is running, negating the benefits of a standardized image. Despite this drawback, many benefits of centralized management remain, including the ability to easily back-up, secure, encrypt, and repair disk images.