SREENIDHI INSTITUTE OF SCIENCE AND TECHNOLOGY(Autonomous Institution, approved by UGC and Accredited by NAAC with ‘A’ Grade)

TECHNICAL SEMINAR

Presented by…Mrinmoy DalalCSE A (13311A0506)

Can a “small” operating system simulate the hardware of some machine so that:• Another operating system can run in that

simulated hardware?• More than one instance of that operating

system run on the same hardware at the same time?

• More than one different operating system can share the same hardware at the same time?

Question

VIRTUAL MACHINES

VIRTUALIZATION

• 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.

• Virtualization hides the physical characteristics of computing resources from their users, be they applications, or end users.

Normal Computer System Virtualized Computer System

HYPERVISOR• Hypervisor is a software program that

manages multiple operating systems (or multiple instances of the same operating system) on a single computer system.

• The hypervisor manages the system's processor, memory, and other resources to allocate what each operating system requires.

• Hypervisors are designed for a particular processor architecture and may also be called Virtualization managers.

WHAT is a Virtual Machine?

„A machine is atool that consistsof one or moreparts, and usesenergy to achievea particular goal.“

-WIKIPEDIA

„A virtual machine (VM) is a simulation of a machine (abstract or real) that is usually different from the target machine (where it is being simulated on).“

-WIKIPEDIA

• The resources of the physical computer are shared to create the virtual machines– CPU scheduling can create the

appearance that each user has own processor

– Spooling and a file system provide • virtual card readers, virtual line printers

– Disk partitioned to provide virtual disks

– A normal user time-sharing terminal serves as the virtual machine operator’s console

Non Virtual Machine Virtual Machine

• Virtual-machine concept provides complete protection of system resources – Each virtual machine is isolated from all other virtual machines.– However, no direct sharing of resources

• Virtual-machine system is a good vehicle for operating-systems research and development. – System development is done on the virtual machine does not

disrupt normal operation– Multiple concurrent developers can work at same time

• The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate to the simulated machine

VM COMPATIBILITY

– Hardware Independent• Physical hardware hidden by the

virtualization layer.– Create Once, Run Anywhere• No Configuration Issues• Migrate VMs between Hosts

– Legacy VMs• Run Ancient OS on new platform• Eg: DOS

EXAMPLE – PAGE TABLES

• Suppose guest OS has its own page tables Then virtualization layer must– Copy those tables to its own– Trap every reference or update to tables and simulate it

• During page fault– Virtualization layer must decide whether fault belongs to guest OS or self– If guest OS, must simulate a page fault

• Likewise, virtualization layer must trap and simulate every privileged instruction in machine!

• Some hardware architectures or features are impossible to virtualize– Certain registers or state not exposed– Unusual devices and device control– Clocks, time, and real-time behavior

VIRTUAL MACHINE MONITOR• Virtual machine monitor (VMM) or

hypervisor is software that supports VMs. It determines how to map virtual resources to physical ones

• Physical resource may be time-shared, partitioned, or emulated in software.

• VMM much smaller than a traditional OS (Isolation portion of a VMM is 10,000 lines of code),

MAIN CONCERN OF VMM

• Biggest problem faced by the VMM is to present the hardware to the VM in a “safe, transparent and efficient way”

• Safe: whatever the VM does, it should not be able to affect other VM’s or the VMM

• Maintain illusion by tricking the software into thinking it has the hardware to itself and by hiding the true state of the hardware

ATTRIBUTES OF VMM

• Encapsulation– VMM manages both software and

hardware thus giving it the ability to manage the hardware resources as well as manipulate and control software stack

• Performance– Overhead is generally transparent for

most workloads, only slowdowns occur for isolation or maintain the transparent illusion of hardware usage levels

Programmers really love to make it complicated ...

Types Of Virtual Machines

Hardware-level virtualization

Operating system-level

High-level language virtual machines

HARDWARE LEVEL VIRTUALIZATION

• Virtualization layer sits right on top of the real hardware

• Since the VM presents a version the real machine, all software written for that hardware (x86) will run on that virtual machine

• Original design from IBM in the 1960’s

OPERATING SYSTEM LEVEL VIRTUALIZATION

• Virtualization layer sit between the operating system and the application programs that run on the operating system

• Virtual Machine runs applications, or sets of applications written for the operating system but in a controlled environment–use host OS API

Real Machine

OS

VMM

Virtual Machine

Application

Applications

HIGH-LEVEL LANGUAGE VIRTUAL MACHINES

• The virtualization layer sits as an application program on top of the operating system

• Can run any programs written for that virtual machine abstraction regardless of the operating system hosting that virtual machine

• Anyone have an example of this?Real Machine

OS

JVM

Java Byte Code

Applications

-Java

WITH GREAT POWER COMES

GREAT EXPLOITS

ATTRIBUTES OF ALL VIRTUAL MACHINES (1)

• Software Compatibility– VM provides compatible abstraction so all software written for the

machine that VM is virtualizing will run on it– Java: “write once, run anywhere”

• Isolation– All software running on the virtual machine is contained within it

and can’t affect other VM’s or processes

ATTRIBUTES OF ALL VIRTUAL MACHINES (2)

• Encapsulation– Virtual machines provide a level of indirection. Any software running within

them can be controlled and manipulated.– Can act like putting a filter on a print service to monitor content or perform

additional book keeping. • Java VM for example can perform run time error checking and garbage collection that C+

+ compiled code can’t do running directly on the hardware

• Performance– Any new software layer adds overhead to system

IMPORTANT USES OF VMs (1)

1. Multiple OSes• No more dual boot!• Can even transfer data (e.g., cut-and-paste) between VMs

2. Protection• Crash or intrusion in one OS doesn’t affect others• Easy to replace failed OS with fresh, clean one

IMPORTANT USES OF VMs (2)

3. Software Management• VMs can run complete SW stack, even old OSes like DOS• Run legacy OS, stable current, test release on same HW

4. Hardware Management• Independent SW stacks can share HW• Run application on own OS (helps dependability)

• Migrate running VM to different computer • To balance load or to evacuate from failing HW

To Sum Up…

• Virtual machines are a number of discrete identical execution environments on a single computer, each of which runs an operating system. This can allow applications written for one OS to be executed on a machine which runs a different OS which provide a greater level of isolation between processes than is achieved when running multiple processes on the same instance of an OS.