Virtual machine

1. Virtual Machine
Virtualization/Emulation

2. What is a virtual machine?
• compute resource that uses software instead of a physical computer to
run programs and deploy apps.
• One or more virtual “guest” machines run on a physical “host” machine.
• Each virtual machine runs its own operating system and functions separately from the other
VMs.

3. Why use a VM?
• Server consolidation- migrating network services and applications from multiple computers
to a singular computer.
• less need to purchase additional physical resources, like hard drives or hard disks, as well as reducing the need for
power, space, and cooling in the datacenter.
• provide additional disaster recovery options by enabling failover and redundancy that could previously only be
achieved through additional hardware.
• Provides an environment that is isolated from the rest of a system.
• no interference
• Testing new applications or setting up a production environment.
• single purpose VM to support a specific process

4. What are VMs used for?
• Building and deploying apps to the cloud.
• Trying out a new operating system (OS), including beta releases.
• New environment to make it simpler and quicker for developers to run dev-test
scenarios.
• Backing up your existing OS.
• Accessing virus-infected data or running an old application by installing an older
OS.
• Running software or apps on operating systems that they weren't originally
intended for.

5. What are the benefits of using VMs?
• Cost savings—reduce your physical infrastructure footprint
• decreasing the need to maintain many servers and saving on maintenance costs and
electricity.
• Agility and speed—Virtualization makes the process of running dev-test
scenarios a lot quicker.
• Lowered downtime—portable and easy to move from one hypervisor to another
on a different machine
• great solution for backup
• Scalability—easily scale your apps by adding more physical or virtual servers to
distribute the workload across multiple VMs.
• increase the availability and performance of your apps.
• Security benefits—allows you to run apps of questionable security.
• safely study computer viruses, isolating the viruses to avoid risking their host computer.

6. Disadvantages of virtual machines
• Running multiple VMs on one physical machine can result in unstable
performance if infrastructure requirements are not met.
• VMs are less efficient and run slower than a full physical computer.
• Most enterprises use a combination of physical and virtual infrastructure to balance the
corresponding advantages and disadvantages.
• A VM can be infected with the weaknesses of the host machine.
• Eg:, process isolation is a feature usually employed by OS. However, there are bugs that
violate it. A regular computer devoid of VMs would then only be affected. But, a computer
with a number of VMs would then infect each of those “machines” as well.

8. Hypervisor
• separates the OS and applications in a computer from the underlying physical
hardware.
• enables virtualization, by giving the physical host machine the ability to operate multiple VMs
on the same system.
• virtualization is inextricably bound to hypervisor technology.
• hypervisors were initially called Virtual Machine Monitors (VMM).
• provides a layer between the hardware and the VMs.
• This layer handles all of the transactions between the two.

9. Types of hypervisors
Type 1
• A type 1 hypervisor is on bare metal. VM resources are scheduled directly to the
hardware by the hypervisor.
• KVM- was merged into the Linux® kernel in 2007
• Critics/Xen Server, VMware ESXi and Microsoft hyper-V
Type 2
• A type 2 hypervisor is hosted. VM resources are scheduled against a host
operating system, which is then executed against the hardware.
• VMware Workstation, Oracle VirtualBox, Microsoft Virtual PC, VMware Workstation, Oracle
Solaris Zones, VMware Fusion, Oracle VM Server