Fundamentals of operating system

1. INTRODUCTION : BASICS OF OPERATING SYSTEMGTU Weightage : 10 marks

Prepared By:Jayesh Chauhan

INTRODUCTION When we need to work with computer we

first switch on the power supply and wait till our system becomes ready to login

System will undergoes to different activities during this period which is called “BOOTING” by which system completes some important warm up tasks that will prepare computer for work.

OS : Definition “An Operating System is software that

manages computer hardware and software resources and provides common services for computer programs”BASIC ARCHITECTURE OF

OS

OS is a software that manages all system activities to perform desired task.

It acts as a interface that communicates commands issued by user application to hardware in hardware understandable form, get work required workdone, collect result and reports back to the user application with desired result in application understandable form.

USER : User uses system to get required work done through user made application

User Application : User uses these software to accomplish certain tasks . Example: MSWORD to prepare documents

BASIC ARCHITECTURE OF OS

System Programs : These are set of programs that belongs to operating system but not used for any system management operations

Example : compiler to convert high level language to low level language

Operating System: OS is a software that manages all operations like i/o managements, memory management, Process management, etc.

Hardware : It is electronic that is used to perform all tasks requested by software layer.

BASIC ARCHITECTURE OF OS

Following steps are performed in booting

BOOTING

Power On Self Test (POST) When we switch on power supply, it

flows toward voltage stabilizer famously known as Switch mode power supply (SMPS)

SMPS wait for fraction of second for voltage to get stabilize and then proceed toward next stage.

Completion of this stage is notified with beep sound.

BOOTING

Following steps are performed in booting

BOOTING

Basic Input Output System (BIOS) POST is followed by device testing

procedure. All the peripheral devices are connected

to computer are tested one by one before they are considered for use which can be notified by blinking of LED of appropriate Device.

example keyboard, Monitor

With successful completion of BIOS system proceed toward the next stage where a most basic program is loaded in main memory(RAM).

BOOTING

BOOTSTRAPING

Operating System program execution After successful loading it is then handed

over to the processor for execution. Complete execution of these program

leads to display of login screen where user needs to provide login credentials.

This basic program is known as “operating System”. Hence we can say that OS does the task of bringing life in machine and converting a dead hardware to usable computer.

BOOTING

1. Convenience : It makes computing convenient, lowering down complexity of manual tasks.

2. Efficient : It makes computing efficient. saving user’s time and money.

3. Ability to evolve : Evolve as a general purpose tool that will cover all possible domains

it can be summarized as : 1. Provides user-friendly interface 2. Make tentative arrangement of

recourses 3. Provides appropriate method for data

storage and communication

Objective Of OS…GTU May..2013

4. Provides reliable and safe environment for execution of user applications.

5. supports user activities through efficient services like

a. For programmer : Availability of utilities that will be use while writing, compiling, executing, testing and debugging programs , example : compiler, debugger

b. For end users : availability of various application programs that will make computing a great experience.

Example : MSoffice

Objective Of OS

Example: It is very normal scenario to see people doing multiple jobs on a computer, like listening to music while browsing through the mail box and downloading some data in the background.

Functions of OS…GTU Dec..13, MAY..14

1. Process management: Simultaneous execution leads to multiple

processes. thus creation, execution and termination of a

process are the most basic functionality of an OS. If processes are dependent, than they may try to

share same resources. thus task of process synchronization comes to the picture.

If processes are independent, than a due care needs to be taken to avoid their overlapping in memory area.

based on priority, it is important to allow more important processes to execute first than others.

these all responsibility will cover by process management


2. Memory management: For every newly created process we need to

provide some space in memory for execution. Allocation and de-allocation of memory to and from

process. Reallocation as per the availability and requirement.

3. File management: If we consider that example of beginning, for a

music player to play song we need to provide song file as input to application

Required file must be existing so that it can be supplied as an input to audio application.


In multiuser system it is quite possible that more than one user may try to access a common file with different intention.

There may be efficient mechanism that will handle such situations to avoid data inconsistency.

1. There must be a facility to manage file operation like create, modify, rename, copy, delete, etc.

2. management of directory structure that will make search operation easy.

3. Protection of data against misuse by providing security.


4. I/O management:consider example stated at beginning , we can see that user taking input using multiple ways , example: mouse is used to browse through mailbox while music player reading data from file and delivering audio output to the speaker. In OS there must be a mechanism that keeps track

of data coming in or going out of system and its appropriate application or device to whom it is intended for I/O management

a. It manages with I/O devices and their drivers b. Managing with device control operations.


5. Security and Protection: We need to protect our data from theft or misuse Different ways for that are: 1. Providing password protection mechanism 2. assigning access right permission to files and

directories.6. User Interface Mechanism User interface is a method that an application

provides for its users to interact with it. There are two methods: a. Command line user interface: where interaction

is done trough console, generally command based.


b. Graphical user interface: where interaction is made by clicking.


1. Batch operating system At beginning around 50’s system used to consume

more set up time. So to overcome this problem it was decided to process the jobs in batches (groups), this technique is known as batch programming.

In this technique jobs of similar type were submitted to CPU for processing and executing together.

These systems mainly focus on automatic execution of the jobs in a batch. This task is carried out under supervisory program known as a ‘Batch Monitor’ program that resided in the lower end of main memory.

Here all jobs are stored in hard disk to create pool of jobs for it’s execution as a batch.

Types of OS…GTU MAY..12, MAY..13, …7 marks

Initially all jobs from job pool are read and executed by the batch monitor. These jobs are grouped by placing identical jobs (jobs with similar needs) in same batch.

Batch processing system than executes these grouped jobs automatically one after another saving its time by undertaking all required activities (like loading, linking) only for once. This resulted in to improved system.

In previously job processing systems all jobs are placed in queue. Jobs were allocated with required memory and when space was available in main memory.

A job was selected from job queue when processor became available , the processor scheduler selects job that was loaded in the memory and execute it.

Types of OS…GTU MAY..12, MAY..13, …7 marks

Fig -System flow diagram

Types of OS…GTU Dec..13, MAY..14

Types of OS…GTU Dec..13, MAY..14

Batch File processingTraditional job processing

This system does not provide any opportunity of user intervention during job execution and all jobs execute on first come first serve basis. There is no scope to provide priority to jobs.

In this system only one job could engage the processor for long time if there was any delay in its input/output operation, the processor time was wasted till the completion of I/O job. This resulted in underutilization of CPU time

Problem with batch system

This method was introduce to overcome the problem of underutilization of CPU and Main memory. Multiprogramming is nothing but interleaved execution of multiple jobs by same computer.

While one program is busy waiting for I/O, Other program is kept ready to utilize the CPU.

Thus CPU time is shared based on status of program under execution at that time.

It is not about execution of jobs at the same instance of time, rather it mean that there only a portion of one is executed than a segment of another.

2. Multiprogramming Operating System

In this figure we can see that at a particular time , If job ‘A’ is not utilizing CPU time because it is busy in I/O options than CPU executes job ‘B’

If same thing is repeated again than another job C is waiting for the CPU for getting its execution time . In this way CPU will never remain idle and will fully utilized for maximum amount of time.

2. Multiprogramming Operating System

Fig :Process of multiprogramming

In This method it is possible to allow many users( user applications) to share the computer resources at same time.

all system resources are allotted on time sharing basis with each process could use resources in a definite time slots.

This creates a scene as if all process are using resources simultaneously.

Aim of time sharing OS is to make interactive use of computer system.

System switches quickly from one user to another , a very short span that is given to each user.

The OS distributes CPU time slots based on number of users trying to execute their tasks. once this time is utilizes control is given to next user on system.

3. Time Sharing Operating System

from figure it is clearly visible that there are five users, out of these all user 5 is active but user 1, user 2, user. 3 and user 4 are in waiting for their turn and user 6 is in ready status.

After user 5 utilizes it’s quantum period, the control moves on to the next ready user as in case user 6. For next stage user 2,user 3, user 4 and user 5 are in waiting state and user 1 is in ready state


Fig :Time sharing system

ADVANTAGES Provides quick response Bring down CPU’s idle time. DISADVANTAGES System has to rely totally on other executing

processes. Must need to take about security and integrity of user

programs and data Problem related to data communication must be

resolved.


Multiprocessor systems with more than on CPU in close communication.

Tightly coupled system – processors share memory, bus, peripheral devices and a clock; communication usually takes place through the shared memory.

I. FEATURES OF MULTIPROCESSOR SYSTEMIt supports large physical address space and larger virtual address space.

II. If one processor fails then other processor should retrieve the interrupted process state so execution of process can continue.

III. Inter-processes communication mechanism is provided and implemented in hardware

IV. Multiprocessor systems are of two types. a. Symmetric Multiprocessing b. Asymmetric multiprocessing

4. MULTIPROCESSOR SYSTEM

Symmetric multiprocessing (SMP) ✦ Each processor runs and identical copy of the operating system.✦ Each processor uses different data and program but sharing some common resources like I/o Devices.✦ Many processes can run at once without performance deterioration. ✦ Most modern operating systems support SMP


Asymmetric multiprocessing (AMP)✦All CPUS are not equal. There is one master processor and remaining are slave processor. Each processor have it’s own memory space.Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. ✦ More common in extremely large systems DIFFERENCE BETWEEN SYMMETRIC AND ASYMMETRIC

MULTIPROCESSING. Symmetric system treats all processors are equals, I/O

can processed on any CPU. Asymmetric multiprocessing has one master CPU and

the remaining CPUs are slaves. The master distributes tasks among the slaves. and I/O is usually done by master.


ADVANTAGES OF MULTIPROCESSOR SYSTEMi. Throughput : Increases because number of processor

is increasesii. Cost : Multiprocessor System is cheaper than the

multiple single processor system.iii. Reliability : If one processor fails , there is no effect on

whole system operation.iv. Response time : less because number of processor are

increased.


Clustered system is a group of computer system connected with a high speed communication link (LAN).

Independent systems, with shared common storage and connected by a high-speed LAN, working together.

Clustering systems are integrated with hardware cluster (supports sharing of high performance disks) and software cluster(In form of unified control of computer system in a cluster work as a server)

Cluster node(server) contains layer of cluster software and run it on the node. Each node(server) monitors the network whether cluster work properly or not

5. CLUSTERED SYSTEM

Fig-General structure of a clustered system

If monitored computer fails than monitoring computer takes control and ownership of it’s storage and other resources and restart application of failed computer

It is divided in to two parts 1. Asymmetric Clustering : Here one machine is always in

stand by mode while other machines running it’s applications.

The stand by machine only monitor the active server. When active server fails the host standby machines takes control and became active server.

2. Symmetric Clustering : More than one servers run the application and uses all available hard disks for operation

5. CLUSTERED SYSTEM

• Distributed Systems consist of multiple, possibly heterogeneous, computers connected together via a network and cooperating in some way, form, or fashion.

• Networks may range from small tight LANs to broad reaching WANs.• WAN = Wide Area Network, such as an international corporation• MAN =Metropolitan Area Network, covering a region the size of

a city for example.• LAN =Local Area Network, typical of a home, business, single-

site corporation, or university campus.• PAN = Personal Area Network, such as the bluetooth connection

between your PC, phone, headset, car, etc.

6. Distributed System

• OS view of the network may range from just a special form of file access to complex well-coordinated network operating systems.

• Shared resources may include files, CPU cycles, RAM, printers, and other resources.


• Advantages • 1. Resource sharing : sharing of software resources like

databases, libraries and hardware resources like CPU cycles, hard disks, RAM, CDROM, printers.

• 2. Higher reliability : Reliability refers to degree of tolerance against errors and component failure. Availability is important aspect of reliability. Availability refers to fraction of time resources available for use. we can increase availability of hard disk by having multiple hard disks so if one hard disk fails or un available , program can use some other hard disks

• 3. Shorter response time and higher throughput.• 4. Incremental growth : to extend power and

functionality of system by simply adding additional resources to system.


An operating system oriented to computer networking, to allow shared file and printer access among multiple computers in a network, to enable the sharing of data, users, groups, security, applications, and other networking functions. Typically over a local area network (LAN), or private network.

In network operating system user can login to remote resources and can access remote resources. there are multiple machines are connected by communication link. User can transfer data from their own machine to remote machine.

Example : Microsoft windows server 2008,Linux

7. Network Operating System

Time constraint is key parameter in RTOS. When user gives an input to system, it must process it

within time limit and result is send back. Real time system fails if it does not give result within the time limits.

A real time kernel is a software that manages time and resources of micro-processor, micro controller and provides services to user applications.

8. Real time Operating System

RTOS

SOFT RTOS

HARD RTOS

Hard real time system :In Hard RTOS critical task

must be completed within time limit

All delay in system is fixed and time bounded.

Existing general purpose OS is does not supports hard RTOS. It can not keep wait for linger time without allotting kernel.

Soft RTOS : It is less restrictive. It can not guarantee that it will able to meet deadline

under all conditions. Example : digital telephone or digital audio APPLICATION AREAS OF RTOS i. transportation : Air traffic control and traffic light

system ii. Communication: digital telephone iii. Detection: radar system iV : Flight simulation : Auto pilot mode In real time system memory management is less

demanding than other types of OS.



Difference between hard and soft RTOSHARD REAL TIME OPERATING SYSTEM

SOFT REAL TIME OPERATING SYSTEM

1. Hard response time is required. 1. Soft response time is required

2. Size of data file is small or medium

2. Size of data file is large.

3. It have little laxity and generally provides full deadline compliance

3.It is more flexible and have greater laxity and can tolerate certain amount of deadline misses

4. Safety critical systems are typically hard real system.

4. Linux is an example of softRTOS

EXPLAIN BASIC SERVICES PROVIDED BY OS ON BARE HARDWARE MACHINE……. GTU, DEC 2014…….7 marks

OS provides different kinds of services to different user programs like load data from memory, allocating disk for storage, file or directory for open and read..

Services provided by OS are:

BASIC SERVICES PROVIDED BY OS

1Program Executtion

2Input Output

Operation

3Error

detection

4File and Directory operation

5Communi

ca-tion

6User

Interface

7Accountin

g

1. Program Execution : before executing the program it is loaded to main memory by OS. Once program loads in main memory it’s execution will be start.

Program may finishes execution with or without error. 2. Input output Operation : program is combination of

input, output statements. while executing programs it requires input , output

devices. OS provides input, output devices to program.

3. Error detection : error detection regarding to memory, CPU, I/O devices.

In user program execution errors may be like memory is full, stack overflow, File not found, Director or file is not exist, printer in not ready, attempt to access illegal memory..


4. File and Directory operations : Os provides services for all operations of user with files and directories like create, modify, rename, delete, search file from directory,

5. Communication :Communication between two processes may be on same machine or two processes of different machine can be done by pipe, shared memory, socket or message passing

shared memory :here one process will create memory portion which the other process can use.

It is faster form of interprocess communication because data does not need to copied between processors.

Socket : it is bidirectional communication device that can be used to communicate with other process on same machine with process running on another machine.

Message passing : Here processes communicates with each other using messages (mails)


6. User interface : User interacts with OS by user interface.

It plays vital role in making use of application simple and effective for operation

It is categorized in to two parts: a. GUI (Graphical user interface) : It is interface where

all commands are tagged to the picture objects. These picture objects can be pointed using input

devices like mouse. It reduces burden of memorizing commands. by GUI non computer savvy will able to use the

application effectively without special guideline. b. Command line user interface: It is another way to issue system commands. Here all operations are carried out using manual

commands.


7. Accounting : It is important task that keeps track of information of

resources and users which types of resources are allocated to which user and whether particular user has permission for this type of resources.


What is system call in OS ? How it is handled by OS?...DEC 2012, MAY 2012, DEC 2014……………7 marks

System call provides interface between running program and kernel of Operating system.

single CPU computer can execute one instruction at a time.

Operating system provides services and system call provides interface to these services.

If process is running of user program and needs a system service such as reading data from file. then it has to execute TRAP function to transfer control from user application to kernel.

By system call program execution in user mode can request kernel’s services.

API(Application Program Interface) is a function definition that describe how to obtain that service and returns integer number for particular system call.

SYSTEM CALL

And this number will be transfer to kernel. kernel is a software program that provides services to input program of operating system like, input, output, memory,CPU

It maintains a table which contains all system call with it’s number. so by matching number from table, it’s corresponding service will be provided.

Result will be send back to user application. as well as it takes parameter of user function either from RAM or from CPU register and control transfers from kernel to user mode.

SYSTEM CALL

…..printf(“hi”);

GCC LIBRARY (API)201

Kernel : write() with output device code

stack “hi”

Monitor

USER SPACE

KERNEL SPACE

1. File management : File management system calls are to create file, close file, read file, write file, get and set file attributes

examples : read(), write(), open(), close(), etc. Every file has some attributes like name of file, type of

file, accounting information, etc.

2. Process management : useful to create, terminate, execute processes

example : fork() – to create process, exit(), wait(), etc.

3. Inter process communication(IPC): pipe, socket, message passing and shared memory are used for IPC

calls : pipe(), shmget() – for shared memory, msg_send(), msg_receive(), socket()

CLASSIFICATION OF SYSTEM CALL

4. I/O management: System calls like request() device and release () device , get and set attributes, read(), write()

5. Information processing and maintenance: set date and time, get time and date, get system data,

get and set processes, files and devices like getpid(), date()

CLASSIFICATION OF SYSTEM CALL

a. simple structure b. Layered approach

1. simple structure Microsoft-Disk Operating system(MS-DOS) is example of

simple structure OS. Most of commercial systems do not have well defined

structure. DOS is small and simple in size, when new versions are introduced, size goes increasing.

There is no CPU execution mode (user and kernel) and so error in application can cause whole system to crash.

MS-DOS consists following layers 1. Application program layer 2.System program layer for resident program

OS STRUCTURE

3. Device driver layer 4. ROM BIOS device driver layer In DOS, application program directly interact with BIOS

driver. If user makes any changes in the BIOS device driver, it creates the problem and affect all system. Here memory size is also limited so after use memory must be made free for other users.

Another example of layered operating system is UNIX operating system.

initially it’s provides limited hardware functionality. UNIX is divided in to two parts : kernel and system programs.

Kernel provides system call for CPU scheduling, file management and memory management. System call uses application program interface in UNIX. API defines set of user interface with set of system programs Kernel supports API and user interface.

OS STRUCTURE

Second type of operating system is layered approach. OS is divided in to number of layers. such layer boundary is properly defined. Bottom layer is called layer 0 and top layer is called layer N. Layer N provides user interface.

A function of layer is also fixed. each layer consists of data structure and set of routines. layer provides services to upper and lower layer.

LAYERED STRUCTURE

First layer (layer 0) contains only basic hardware to implement function. so only first layer is debugged for checking whole system. If error not found then the system will work properly. If error encounters while debugging second layer, then error is related to second layer only.

Care should be taken while designing the layers. which functions are added to which layer must be designing properly. some of the functions included only in lower level. Device driver, memory management and input output operation function must be included in lower level.

Secondary storage will required for all operations, when CPU changes the process as per scheduling method, currently executing process is stored o secondary storage. DISK space is required for this purpose. So CPU scheduling is includes in the above layer of the secondary storage.

LAYERED STRUCTURE

Advantages of Layered Approach: 1. Modularization makes debugging much easier. 2. Simple to design and implement 3. Provides transparency between layers DISADVANTAGES OF LAYERED APPROACH 1. less efficient because system call takes longer time 2. Interaction between layers and parameter passing is

difficult.

LAYERED STRUCTURE

Kernel is a software code that reside in central core of OS. It has complete control over system.

Kernel does not interact directly with user, But it interacts using SHELL and other programs and hardware. When operation system boots, kernel is first part of

OS to load in main memory. Kernel remains in main memory for entire duration of computer session. The kernel code is usually loaded in to protected area of memory.

Kernel performs it’s task like executing processes and handling interrupts in kernel space. User performs it’s task in user area of memory. This memory separation is made in order to prevent user data and kernel data from interfering with each other.

Kernel

When computer crashes, it actually means kernel has crashed. Single program crash is not a kernel crash. kernel provides services for process management, file management, i/O management, memory management. System calls are used to provide this type of services.

Kernel includes a. Scheduler : allocates the kernel’s processing time to

various processes. b. Supervisor : it grants permission to use computer

system resources to each process. 3. Interrupt handler : handles all requests from the

various hardware devices which compete for kernel services.

4.Memory manager : allocates space in memory for all users of kernel service.

Kernel

Types of kernel 1. Monolithic kernel 2. Micro kernel 3. Hybrid kernel 4. Exo-kernel

Kernel

Traditional UNIX OS uses monolithic kernel. The entire OS runs as a single program in kernel mode. Program contains operating system core function and device driver.

In this approach, most of operations performed by kernel via system call. LINUX OS uses modern monolithic kernel architecture. It loads the modules at run time.

Monolithic Kernel

USER APPLICATIONS

COMPUTER HARDWARES

FILEI/O

Memory

MgmtProcess

I/ODriver

s

Memory

Manager

Interrupt driver

Advantages : 1. simple to design and implement 2. It provides speed on hardware Dis-advantages: 1. If code size increases, difficult to maintain. 2. Fault tolerance is low.

Monolithic Kernel

Microkernel provides minimal services like defining memory address space, IPC and process management.

It is small operating code. Hardware resource management is implemented whenever process is executing. The function of microkernel is to provide a

communication facility between the client programmers. For communication it uses message passing method.

Microkernel runs in kernel mode and rest run in normal user processes. It is also provides more security and reliability. Most of services are running as user rather than kernel processes.

here device driver and file system running as separate user processes, a error in one can crash only single componenet.

Micro Kernel

here device driver and file system running as separate user processes, a error in one can crash only single component.

Advantages: 1. allows addition of new services 2. Supports objects oriented OS 3.Modular design helps to enhance reliability. 4.It lends it self to distributed system support 5. microkernel architecture support flexibility. User

can add or subtract services according to requirement.

Micro Kernel

Comparison between monolithic and microkernelMonolithic Kernel Micro kernel

1. Kernel size is large 1. Kernel size is small

2. OS is complex to design 2. OS is easy to design, implement and install

3. Request may be serviced faster

3.Request may be serviced slower than monolithic kernel

4. All the operating system services are included in kernel

4. Kernel provides only IPC and low level device management services.

5. No message passing, no context switching required while kernel is performing job.

5. It requires message passing and context switching.

If several processes enters in kernel mode at same time, A reentrant kernel is able to suspend the current running process even if process is in kernel mode.

With reentrant kernel the scheduler will assign CPU to another process until interrupt from disk controller indicates that data is available and the earlier thread can be resumed

If hardware interrupts occurs, a reentrant kernel is able to suspend current running process if that process is in kernel mode. which improves the throughput of the device controllers that issues inputs.

Once device has issued interrupt, it waits until the CPU acknowledges. If the kernel is able to answer quickly, the device controller will be able to perform other tasks while CPU handles the interrupt.

Reentrant Kernel

Virtualization means it is looking something different than existing.

Virtualization deals with extending actual interface so as to mimic the another system.

Example VMWARE, XEN,Virtual Private network

Virtual memory : Consider following figure which contains one memory block which contains 1 to 100 blocks

Virtual Machine

Here user see is this system something different

1

100

…

1

1000

… but actually the memory is from 1…1000.there are 10 users but they had maintained one user interface based on this (all have slot from 1..10)

When user 1 writes data on memory he can uses location from 1 to 100. and it will be written actually in first 1…to 100 location of actual memory

Whenever user 2 writes something on it’s location 5, it is basically written to memory location 105 of actual memory, but here user 2 thinks that he is writing in line 5..this is called virtualization of memory

Virtual Machine

Here in physical machine CPU executes your process, memory is used to store data, NIC (network interface card is used to perform networking task and RAM contains faster memory inform of stack)

Physical hardware are processors, memory, I/O bus, devices

Most of time in PC resource utilization is generally 5% to 10% which is very less and it leads to under-utilization of resources.

this problem arises because of hardware is tightly coupled with operating system and there will be only one OS that controls all

hardware resources one at a time.

time Virtual Machine

Virtual Machine

If we remove OS from here and add abstract layer of virtualization and divide hardware in to two parts for two virtual machines which have their own OS.Here these hardware are not physical H/w but these are virtual h/w .Virtual h/w: processors,

Vitual Machine architecture

In different virtual machine you can have different OS like in machine 1 you have Linux and in machine 2 you have Windows

Whenever OS try to access CPU it will see it’s virtual CPU, if OS pass command to execute process, virtual CPU send it to actual CPU but now actual CPU is also shared by another Virtual OS/Machine

If you have 100% utilization than 50% CPU cycles given to VM1 and other 50% given to VM2.

If VM1 utilizes 25% cycles out of 50% and VM2 utilizes 0 cycles out of 50% than we can say that total utilization is 25% but VM1 thinks that total utilization is 50%.

It provides secure multiplexes of hardware resources

Virtual Machine

VM1 VM2 VM3 VM40.25 0.25 o.25 0.25

If host contains 4 virtual machines than 4 parts of 1 second given to each CPUs

Advantages: provides strong guarantees if one of virtual machine

infected by virus, software bugs or crashes, it does not affect other VMs.

It increases resource utilization because of multiplexing.

Virtual Machine

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Engineering

Fundamentals of operating system