Since the 90’s VMware has been evolving. It started as a clumsy little software that used to be installed on a Windows desktop. Then from there, it changed into GSX for Windows Servers. And then again it morphed into ESX which eliminated the need for Windows and booted to a Redhat kernel. And later in version 4, it became ESXi which now runs on a custom Linux kernel.
A couple of years ago I remembered going to a demo and watching Hyper-V crash, but since then a lot has changed. Hyper-V can now do many of the same things most enterprise virtualization software boast about. Live migration, HA, templates, and importing VMs from VMware and EC2 using SystemCenter VMM. The only real hang up is the lack of popularity with the Linux community
Partitioning a single server to appear as multiple servers has been increasingly common on microcomputers since the launch of VMware ESX Server in 2001. The physical server typically runs a hypervisor which is tasked with creating, releasing, and managing the resources of "guest" operating systems, or virtual machines. These guest operating systems are allocated a share of resources of the physical server, typically in a manner in which the guest is not aware of any other physical resources save for those allocated to it by the hypervisor. As a VPS runs its own copy of its operating system, customers have superuser-level access to that operating system instance, and can install almost any software that runs on the OS; however, due to the number of virtualization clients typically running on a single machine, a VPS generally has limited processor time, RAM, and disk space.