Virtualization

Virtualisation is the creation of virtual instances of computers or operating systems on a single physical machine. These virtual instances are commonly known as Virtual Machines or “VMs”. Virtual Machines share the resources of that single computer across multiple environments. Different virtual machines can run different operating systems and multiple applications on the same physical computer.

How Does Virtualization Work

• Virtualization uses software called a hypervisor such as VMware ESX Server or Microsoft Hyper-V to “virtualize” the hardware resources of an x86-based computer—including the CPU, RAM, hard disk and network controller—to create a fully functional virtual machine that can run its own operating system and applications just like a “real”, physical computer.
  
• Each virtual machine contains a complete system(BIOS, CPU, RAM, Hard Disks, Network Cards) eliminating potential conflicts.
  
• Virtualization works by inserting a thin layer of software directly on the computer hardware or on a host operating system. This contains a virtual machine monitor or hypervisor that allocates hardware resources dynamically and transparently.
  
• Multiple operating systems run concurrently on a single physical computer and share hardware resources with each other.
• By encapsulating an entire machine, including CPU, memory, operating system, and network devices, a virtual machine is completely compatible with all standard x86 operating systems, applications, and device drivers.

Hypervisor

A hypervisor is hardware virtualization software that allows multiple virtual machine to run on a single physical computer. A hypervisor is also called virtual machine monitor or "VMM".

Types of Hypervisors

There are two types of hypervisors, Hypervisor Type 1 (native, bare-metal) and Hypervisor Type 2 (hosted).

• A Type 1 (or native, bare-metal) hypervisor is a thin layer of software that runs directly on the physical host's hardware. It manages physical resources and also the interaction between the physical hardware and virtual machines. It is also responsible for monitoring the guest operating systems inside the virtual machines. A guest operating system (such as Microsoft Windows Server 2003 or Microsoft Windows XP Professional) thus runs on another level, above the hypervisor. This is the classic implementaion of virtual architectures. Examples of type 1of hypervisors are:
  • VMware ESX Server
  • Oracle VM
  • Microsoft Hyper-V
  • Xen
  • Citrix XenServer

• A Type 2 (or hosted) hypervisor is a software application that runs withing a conventional operating system environment. Considering the hypervisor layer being a distinct software layer, guest operating systems thus run at the third level above the hardware. Examples of Tye 2 hypervisors are:
  • VMware Server (formerly known as GSX)
  • VMware Workstation
  • Vmware Fusion
  • Microsoft Virtual PC
  • Microsoft Virtual Server
  • Sun xVM VirtualBox