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The hypervisor sets up isolated execution environments, each of which has its own set of abstracted hardware resources such as memory, disk, processor and network adapter(s). It is this bundling of abstracted hardware that is really a virtual machine capable of sharing physical hardware with other virtual machines because it believes it has exclusive access to the hardware. The hypervisor manages the way virtual machines access hardware (Hales, Eiler, & Jones, 2013), and provides the virtual machines with the illusion that they are in fact running on physical hardware, which they are not (Arrasjid, Epping, & Kaplan, 2010). More recently changes are being made to the operating systems themselves to make them aware that they are running on virtual rather than physical hardware, so as to improve performance of virtual machines and remove some of the overhead associated with virtualization.
As Microsoft (2012a) put it, the hypervisor is really the layer of software that interacts with the hardware and lies below one or more operating systems. These guest operating systems, or virtual machines as they are more commonly known, are in every way the same as machines installed on physical computers except that they run on the virtualized hardware presented to them by the hypervisor. As a result of these isolated execution environments one virtual machine can fail without it affecting other running virtual machines. Naturally dependencies may exist, whereby a web server might require a database server and if the database server fails, so will the delivery of data to the web server. This, though, has nothing to virtualization and would occur whether machines are virtualized or not (Williams & García, 2007).
Key Terms in this Chapter
vCenter: A VMware application designed to manage VMware hosts, which is installed on a Windows server.
Hypervisor: Software that interacts directly with hardware and presents an abstract form of that hardware to the virtual machines.
ESXi: VMware’s current server-based hypervisor based on Red Hat Linux.
VMware: A leading multinational corporation with headquarters in Palo Alto, California and the brand most strongly associated with virtualization.
vCloud Director: A VMware application that enables one to build private clouds through the use of one or more vCenter servers.
Hyper-V: Microsoft’s current server-based hypervisor included in various Windows server operating systems.
System Center: A Microsoft server application used to manage multiple hypervisors as well as physical resources and a range of applications.
Virtualization: A logical view of a computing resource, in many cases a computer but also possibly storage or networking.
Virtual Machine: A guest system with a set of abstract hardware, including virtual memory, virtual network adapters, and virtual disks.
Microsoft: A leading multinational corporation with headquarters in Redmond, Washington, which is associated especially with its Windows operating system and applications such as Microsoft Office.
Host: A physical computer with a hypervisor installed capable of hosting one or more guest virtual systems otherwise known as virtual machines.