The greatest challenge to any thinker is stating the problem in a way that will allow a solution

Bertrand Russell

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On 23 Mar 2013

Basic / Introductionary

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Or more specifically, how does server or desktop computer virtualisation work?

The purpose of virtualisation is to enable to be able to run more things on less hardware.  To allow you to run numerous virtual instances of a machine on a single computer.  But how do you do that?

Physical world

Physical world – a standard computer looks like this

The Physical World

In the traditional physical world each physical computer runs one dedicated Operating System (OS). On top of that OS, you can run one or more applications. Your desktop or laptop computer (or tablet or smartphone) work like this. Its also how traditional servers operate.

The Operating System is installed on the machine and it stays there. It cannot be easily moved to another machine, nor can you install another OS to run at the same time on the same machine without removing/overwriting/destroying the original OS.

One machine, one Operating System.

The Virtualised World

Virtual world

Virtual world – multiple operating systems mean we have multiple (virtual) computers sitting on the same piece of physical computer hardware

Here we want to be able run multiple Operating Systems on the same physical machine. To do this we first need to an extra layer of software, on top of the hardware. This extra bit of software allows you to run multiple Operating Systems on the same piece of hardware, and is known as the Hypervisor.

The Hypervisor acts a broker, divvying up access to the physical hardware to the Operating Systems. Think of it as a waitress serving lots of customers in a busy restaurant. The hardware is the kitchen, the engine room of the operation. The Operating Systems are the individual restaurant tables, with hungry Applications on them wanting to be served. The waitress/hypervisor runs around serving food and drinks to the tables/Operating Systems.

With the Hypervisor in place we can then install multiple Operating Systems. Each instance of an Operating System is effectively a different computer, this more commonly known a Virtual Machine (VM).

Reign of the Virtual Machines

Virtual Machines

Virtual Machines – Each instance of an OS makes up a Virtual Machine (a VM)

Now we can install many virtual computers into one physical host computer. Many Virtual Machines (or VMs) on to one physical host machine.

This means its possible to make huge savings in the cost of purchasing and supporting computer hardware. Instead of supporting one computer, each machine can now support many (100’s – depending on the type of hypervisor and hardware used).

The magical hypervisor, that allows it all to happen, is available from the current market leader, VMware, for free (they charge for additional features such as being able to cluster lots of physical hosts together). They, VMware, also have plenty of healthy competition from the likes of Microsoft, Citrix and others; who have similarly free and premium offerings.

The age of the expensive monolithic physical machine has long past, now is the age of the virtual machines.


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