Editor’s note: With all the talk about cloud computing and cloud systems, many are still wondering if this type of system is actually ‘in the clouds’. Sharon provides an excellent background as well as history to the introduction of the mechanisms that made cloud computing possible – the virtual machine. After reading her article, you should be comforted by the fact that you won’t have a computer system come crashing down on you from the skies… should it crash from lack of electricity as would any computer, however, is another story! 🙂
Since 1998, when VMware Inc. first jumped into the virtualization business, virtual technology has completely revolutionized data center technology, not to mention the business models of those companies who’ve adopted the technology over the years.
But what exactly is a virtual machine?
How does it relate to virtualization, and what are the benefits of system virtual machines versus process virtual machines?
Types of Virtual Machines and How They Work
Though a bit dated, this comprehensive article, The Rise of the Virtual Machines, from TechTarget, outlines the basics of virtualization and virtual machines.
There are two major types of virtual machines…
- process virtual machines and
- system virtual machines.
A process virtual machine, sometimes called an application virtual machine, runs as a normal application inside an operating system and supports a single process.
It is created when that process is started and destroyed when that process is finished.
Its purpose is to provide a platform-independent programming environment that abstracts away details of the underlying hardware or operating system, and allows a program to execute in the same way on any platform.
A system virtual machine (also known as a hardware virtual machine) is the most common kind of virtual machine, and what most IT folks think of when they hear the term ‘virtualization’ or ‘virtual machine.
It allows the sharing of the underlying physical machine resources among different virtual machines, whereas each has its own operating system.
Individual virtual machines run on the same physical machine.
The software layer providing the virtualization is called a virtual machine monitor or hypervisor.
Origins of Virtual Machines
The technology got its start on mainframes decades ago, but VMware was able to migrate the technology from mainframes to the x86 platform and the little startup almost immediately became a technology superstar.
Virtualization allows IT departments to run several applications on the same server, each isolated into virtual operating system images that wouldn’t affect each other. Doing so cut costs, increased efficiency and freed IT administrators from the laborious task of maintaining huge server farms.
A virtual machine is, in the words of the pioneer, VMware, a tightly isolated software container that can run its own operating systems and applications as if it were a physical computer.
A virtual machine behaves exactly like a physical computer and contains it own virtual (ie, software-based) CPU, RAM hard disk and network interface card (NIC).
Advantages of the Virtual Machine
Since a virtual machine isn’t actually made up of physical hardware, the technology offers a number of advantages.
Since a virtual machine hosts its own operating system and applications, and has all the components found in a physical computer, they are completely compatible with all standard x86 operating systems, applications and device drivers, so you can use a virtual machine to run the same software that you would on a physical x86 computer.
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While virtual machines can share the physical resources of a single computer, they remain completely isolated from each other as if they were separate physical machines.
If, for example, there are 4 virtual machines on a single physical server and one of the virtual machines crashes, the other 3 virtual machines remain available.
Isolation is an important reason why the availability and security of applications running in a virtual environment is far superior to applications running in a traditional, non-virtualized system.
A virtual machine is essentially a software container that encapsulates a complete set of virtual hardware resources, as well as an operating system and all its applications, inside a software package.
Encapsulation makes virtual machines incredibly portable and easy to manage.
If you wanted, you could move and copy a virtual machine from one location to another just like any other software file, or save a virtual machine on any standard data storage medium, from a pocket-sized USB flash memory card to an enterprise storage area network (SAN).
Virtual machines are completely independent from their underlying physical hardware.
For example, you can configure a virtual machine with virtual components that are completely different from the physical components present on the underlying hardware.
Virtual machines on the same physical server can even run different kinds of operating systems.
This capability gives you the freedom to move a virtual machine from one type of x86 computer to another without making any changes to the device drivers, operating system or applications.
Hardware independence also means that you can run a heterogeneous mixture of operating systems and applications on a single physical computer.
Virtual machines are the building blocks of virtualization, and both are components of a much larger solution: the virtual infrastructure.
While a virtual machine represents the hardware resources of an entire computer, a virtual infrastructure represents the interconnected hardware resources of an entire IT infrastructure—including computers, network devices and shared storage resources.
Combining virtual servers and desktop virtualization infrastructures that improve the availability, security and manageability of mission-critical applications is the new frontier for enterprises looking to increase efficiency and reduce costs.
Share with us in the comments section below what additional thoughts you have to the beginnings of the cloud system, perhaps you have something we have overlooked?
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Sharon is a Senior Writer at CIO.com at IDG Enterprise (CIO Magazine) in the Greater Philadelphia Area, focused on Writing and Editing.
Sharon occasionally blogs for cloud provider Rackspace Hosting.
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