An Introduction to Virtualization

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  PraveenKumar Purushothaman

  Virtualization Defined
  
  Virtualization refers to the process of decoupling the hardware from the operating system on a physical machine. It turns what used to be considered purely hardware into software. Put simply, you can think of virtualization as essentially a computer within a computer, implemented in software. This is true all the way down to the emulation of certain types of devices, such as sound cards, CPUs, memory, and physical storage. An instance of an operating system running in a virtualized environment is known as a virtual machine. Virtualization technologies allow multiple virtual machines, with heterogeneous operating systems to run side by side and in isolation on the same physical machine. By emulating a complete hardware system, from processor to network card, each virtual machine can share a common set of hardware unaware that this hardware may also be being used by another virtual machine at the same time. The operating system running in the virtual machine sees a consistent, normalized set of hardware regardless of the actual physical hardware components. Technologies such as Intel® Virtualization Technology (Intel® VT), significantly improves and enhances virtualization from the perspective of the vendors that produce these solutions.
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  PraveenKumar Purushothaman

  Terminologies Used
  
  Terminologies Used
  
  Individual vendors often choose terminology that suits their marketing needs to describe their products. Like the nuances of the virtualization technologies, it’s easy to get confused over the different terms used to describe features or components. Hopefully as virtualization technology continues to evolve and as more players enter the marketplace, a common set of terminology will emerge. But for now, here is a list of terms and corresponding definitions.
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  PraveenKumar Purushothaman

  Re: Terminologies Used
  
  Host Machine
  
  A host machine is the physical machine running the virtualization software. It contains the physical resources, such as memory, hard disk space, and CPU, and other resources, such as network access, that the virtual machines utilize.
  
  Virtual Machine
  
  The virtual machine is the virtualized representation of a physical machine that is run and maintained by the virtualization software. Each virtual machine, implemented as a single file or a small collection of files in a single folder on the host system, behaves as if it is running on an individual, physical, non-virtualized PC.
  
  Virtualization Software
  
  Virtualization software is a generic term denoting software that allows a user to run virtual machines on a host machine.
  
  Virtual Disk
  
  The term refers to the virtual machine’s physical representation on the disk ofthe host machine. A virtual disk comprises either a single file or a collection of related files. It appears to the virtual machine as a physical hard disk. One of the benefits of using virtual machine architecture is its portability whereby you can move virtual disk files from one physical machine to another with limited impact on the files.
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  PraveenKumar Purushothaman

  Re: Terminologies Used
  
  Virtual Machine Additions
  
  Virtual machine additions increase the performance of the guest operating system when compared to running without the additions, provide access to USB devices and other specialized devices, and, in some cases, to higher video resolutions than without the additions, thus offering an i improved user interface experience within a virtual machine. The additions also allow the use of customizations such as shared folders, drag -and-drop copy and paste between the host and virtual machines and between virtual machines, and other enhancements.
  
  One particularly useful enhancement is the ability of the mouse pointer’s focus to naturally move from the virtual machine window to the host machine’s active application windows without having to physically adjust it each time the window changes. This allows you to interact with the virtualized operating system as if it were nothing more than another application window, such as a word processing program running on the host machine.
  
  Shared Folders
  
  Most virtual machine implementations support the use of shared folders. After the installation of virtual machine additions, shared folders enables the virtual machine to access data on the host. Through a series of under-the-cover drive mappings the virtual machine can open up files and folders on the physical host machine. You then can transfer these files from the physical machine to a virtual machine using a standard mechanism such as a mapped drive.
  
  Shared folders can access installation files for programs, data files, or other files that you need to copy and load into the virtual machine. With shared folders you don’t have to copy data files into each virtual machine. Instead, all of your virtual machines access the same files through a shared folder that targets a single endpoint on the physical host machine.
  
  Virtual Machine Monitor (VMM)
  
  A virtual machine monitor is the software solution that implements virtualization to run in conjunction with the host operating system. The virtual machine monitor virtualizes certain hardware resources, such as the CPU, memory, and physical disk, and creates emulated devices for virtual machines running on the host machine. For now, it is important to understand that the virtual machine monitor determines how resources should be allocated, virtualized, and presented to the virtual machines running on the host computer. Many software solutions that exist today utilize this method of virtualization.
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  PraveenKumar Purushothaman

  Architecture of a Virtual Machine
  
  

  Architecture of a Virtual Machine
  
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  PraveenKumar Purushothaman

  Reasons for Using Virtualization
  
  Generally it is used only for servers. The main reasons include:
  
  » Space Compactness: Physical space can be saved by installing many virtual servers in a single physical server.
  
  » Backup & Restore: If we need to provide a dedicated server for just backup purposes, it will cost a lot. The same can be avoided using virtualisation and also since both the main system and the backup server resides on a same physical hardware, the transfer of files and backing up will be faster.
  
  » Testing Purposes: As we all know, if we need to install and test something, it will surely make our system's performance go down. So, instead of physically testing them, we can do it virtually, without causing any physical problem to the hardware. Something like, formatting a HDD for 100 times will cause the physical HDD fail, also switching from one file system to another, namely FAT32 to Ext2, etc., will have serious impact. Remember Non Destructive Testing in Physics?
  
  » Migration: One main factor in Server Systems is Migration. Remember what happened to CE Servers, when some new article was posted? It was unable to tolerate the load and it got down. At these instances, new or upgraded hardware is required. If we have the server running in the virtual machine, it is easy to migrate from the old system to the new system. If not, you need to install the same configuration and software, in order to bring the same old server again.
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  durga ch

  Great Article Praveen! 😀
  
  As my 2 cent, I can quote an example to exemplify whats written here.
  One of my friend was doing some kind of network related performance testing . When asked he told me he was using whole lab environment emulated some where in US, which had distrubuted nodes in hundreds of number.
  He was testing it sitting at one of the desks in Sydney 😀.
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  PraveenKumar Purushothaman

  @Durga the credits go to you, as you were the one, who motivated me to start an article on Virtualization... More to come, the types of VMs, etc...