Virtualization refers to the act of creating a virtual (rather than actual) version of something, including virtual computer hardware platforms, operating systems, storage devices, and computer network resources. Hardware virtualization or platform virtualization refers to the creation of a virtual machine that acts like a real computer with an operating system. Software executed on these virtual machines is separated from the underlying hardware resources. For example, a computer that is running Microsoft Windows may host a virtual machine that looks like a computer with the Ubuntu Linux operating system; Ubuntu-based software can be run on the virtual machine

1. Operating System 16
Virtual Machines
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. Virtualization
• Virtualization refers to the act of creating a virtual (rather
than actual) version of something, including virtual
computer hardware platforms, operating systems, storage
devices, and computer network resources.
• Hardware virtualization or platform virtualization refers to
the creation of a virtual machine that acts like a real
computer with an operating system.
• Software executed on these virtual machines is separated
from the underlying hardware resources.
• For example, a computer that is running Microsoft
Windows may host a virtual machine that looks like a
computer with the Ubuntu Linux operating system;
Ubuntu-based software can be run on the virtual machine.

3. Hardware Virtualization
• In hardware virtualization, the host machine is
the actual machine on which the virtualization
takes place, and the guest machine is the
virtual machine.
• The words host and guest are used to
distinguish the software that runs on the
physical machine from the software that runs
on the virtual machine

4. Layers as base of Virtualization
• Conceptually, a computer system is made up of layers.
• The hardware is the lowest level in all such systems.
• The kernel running at the next level uses the hardware instructions
to create a set of system calls for use by outer layers.
• The systems programs above the kernel are therefore able to use
either system calls or hardware instructions, and in some ways
these programs do not differentiate between these two.
• Thus, although they are accessed differently, they both provide
functionality that the program can use to create even more
advanced functions.
• System programs, in turn, treat the hardware and the system calls
as though they both are at the same level.

5. Layered to VM
• Some systems carry this scheme even a step further by
allowing the system programs to be called easily by the
application programs.
• As before, although the system programs are at a level
higher than that of the other routines, the application
programs may view everything under them in the hierarchy
as though the latter were part of the machine itself.
• This layered approach is taken to its logical conclusion in
the concept of a virtual machine.
• The VM operating system for IBM systems is the best
example of the virtual-machine concept, because IBM
pioneered the work in this area.

6. Virtualization Implementation
• By using CPU scheduling and virtual-memory techniques,
an operating system can create the illusion of multiple
processes, each executing on its own processor with its
own (virtual) memory.
• Of course, normally, the process has additional features,
such as system calls and a file system, which are not
provided by the bare hardware.
• The virtual-machine approach, on the other hand, does not
provide any additional function, but rather provides an
interface that is identical to the underlying bare hardware.
• Each process is provided with a (virtual) copy of the
underlying computer.

7. Resource Sharing
• The resources of the physical computer are
shared to create the virtual machines.
• CPU scheduling can be used to share the CPU and
to create the appearance that users have their
own processor.
• Spooling and a file system can provide virtual
card readers and virtual line printers.
• A normal user timesharing terminal provides the
function of the virtual machine operator’s
console.

8. Multi User System
• Users thus are given their own virtual machine.
• They can then run any of the operating systems or software
packages that are available on the underlying machine.
• For the IBM VM system, a user normally runs CMS, a single-
user interactive operating system.
• The virtual-machine software is concerned with
multiprogramming multiple virtual machines onto a
physical machine, but does not need to consider any user-
support software.
• This arrangement may provide a useful partitioning of the
problem of designing a multiuser interactive system into
two smaller pieces.

9. Assignment
• Explain the concept of Virtual Machine and
briefly describe its implementation.