A virtual machine (VM) uses software to run programs and deploy apps instead of using physical computer hardware. Multiple VMs can run on a single physical host machine. Each VM runs its own operating system separately from other VMs. VMs provide benefits like cost savings, agility, scalability, and security by isolating applications. However, VMs can also result in slower performance compared to physical machines. A hypervisor manages interactions between the physical hardware and VMs, enabling virtualization. There are two main types of hypervisors - type 1 runs directly on the hardware while type 2 runs within a host operating system.

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