Virtual Machines

UNIT V: Virtual Machines and Mobile OS

Chapter 7: Virtual Machines and Mobile OS

Syllabus

Virtual Machines - History, Benefits and Features, Building Blocks, Types of Virtual Machines and their Implementations, Virtualization and Operating-System Components; Mobile OS - iOS and Android.

Virtual Machines

• Virtual Machine (VM) is virtual environment that functions as a virtual computer system with its own CPU, memory, network interface, and storage, created on a physical hardware system.

• A Virtual machine is a software construct that mimics the characteristics of a physical server.

• A virtual Machine (VM) is a software program or operating system that not only exhibits the behavior of a separate computer, but is also capable of performing tasks such as running applications and programs like a separate computer.

• In a pure virtual machine architecture the operating system gives each process the illusion that it is the only process on the machine. The user writes an application as if only its code were running on the system.

• Each user interacts with the computer by typing commands to the virtual machine on a virtual system console and receiving results back from the machine as soon as they are computed.

• Each user directs the virtual machine to perform different commands. These commands are then executed on the physical machine in a multiprogramming environments.

• Virtualization is an abstraction layer that decouples the physical hardware from the operating system to deliver greater IT resource utilization and flexibility.

• It allows multiple virtual machines, with heterogeneous operating systems to run in isolation, side-by-side on the same physical machine..

Fig. 7.1.1 shows virtual machine.

Benefits:

1. There is no overlap amongst memory as each Virtual Memory has its own memory space.

2. Virtual machines are completely isolated from the host machine and other virtual machines.

3. Data does not leak across virtual machines.

4. Can use multiple operating system environments on the same computer

5. The cost reduction is possible using small virtual servers on a more powerful single server.

Disadvantages :

1. Virtual machines are less efficient than real machines because they access the hardware indirectly.

2. A virtual machine can be infected with the weaknesses of the host machine

3. Difficulty in direct access to hardware, for example, specific cards or USB devices

4. Great use of disk space, since it takes all the files for each operating system installed on each virtual machine.