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INTRODUCTION TO OPERATING SYSTEMS
Summer Semester 2013
Intro To OS, Lecture 1 By Rana Umer
Rana Umer Aziz
MSc.IT (London, UK)
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Intro To OS, Lecture 1 By Rana Umer
EDUCATION CONSULTANT
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Intro To OS, Lecture 1 By Rana Umer
Book
MODERN OPERATING SYSTEMS
Third Edition By
ANDREW S. TANENBAUM
Course Outline
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Introduction
Processes & Threads
Memory Management
File Systems
Input / Output
Deadlocks
Multimedia Operating Systems
Multiple Processor Systems
Case Study 1: LINUX
Case Study 2: Windows Vista
Intro To OS, Lecture 1 By Rana Umer
Outline
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What is an operating system
The history of Operating System
Hardware of operating system
Important concepts of Operating System
Intro To OS, Lecture 1 By Rana Umer
What is an operating system
• An Operating System is a program that acts as
an intermediary/interface between a user of a
computer and the computer hardware.
• OS goals:
– Control/execute user/application programs.
– Make the computer system convenient to use.
– Ease the solving of user problems.
– Use the computer hardware in an efficient
manner
Intro To OS, Lecture 1 By Rana Umer
Operating System
A modern computer consists of:
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One or more processors
Main memory
Disks
Printers
Various input/output devices
Managing all these components requires a layer of
software – the operating system
Intro To OS, Lecture 1 By Rana Umer
Operating System
• A modern computer is very complex.
– Networking
– Disks
– Video/audio card
• It is impossible for every application programmer
to understand every detail
• A layer of computer software is introduced to
provide a better, simpler, cleaner model of the
resources and manage them
Intro To OS, Lecture 1 By Rana Umer
Operating System
Intro To OS, Lecture 1 By Rana Umer
Operating System
• Users use various OS
– Windows, Linux, Mac OS etc.
• User interacts with shell or GUI (Graphical
User Interface )
Intro To OS, Lecture 1 By Rana Umer
Operating System
• On top of hardware is OS
• Most computers have two modes of operation:
– Kernel mode and user mode
– OS runs in kernel mode, which has complete
access to all hardware and can execute any
instruction
– Rest of software runs in user mode, which has
limited capability
– Shell or GUI is the lowest level of user mode
software
Intro To OS, Lecture 1 By Rana Umer
Operating System
• The kernel is the main component of most computer operating
systems it is a bridge between applications and the actual data
processing done at the hardware level. The kernel's responsibilities
include managing the system's resources (the communication
between hardware and software components).
Intro To OS, Lecture 1 By Rana Umer
The Operating System as an Extended
Machine
Intro To OS, Lecture 1 By Rana Umer
As an Extended Machine
• Abstraction:
– CPU—process
– Storage –- files
– Memory– address space
• 4 types of people:
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Industrial engineer: design hardware
Kernel designer
Application programmer: OS’s user
End users
Intro To OS, Lecture 1 By Rana Umer
The Operating System as a Resource Manager
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Allow multiple programs to run at the same time
Manage and protect memory, I/O devices, and other
resources
Includes multiplexing (sharing) resources in two
different ways:
• In time
• In space
Intro To OS, Lecture 1 By Rana Umer
As Resource Manager
• Modern OS runs multiple programs of
multiple users at the same time
– Imagine what would happen if several programs
want to print at the same time?
– How to account the resource usage of each
process?
– Resources can be multiplexed:
• How to ensure fairness and efficiency?
Intro To OS, Lecture 1 By Rana Umer
History of Operating Systems
Generations:
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First Generation (1945–55) Vacuum Tubes
2nd Generation (1955–65) Transistors and Batch
Systems
3rd Generation(1965–1980) ICs and
Multiprogramming
4th Generation(1980–Present) Personal Computers
5th Generation (Artificial Intelligence)
Intro To OS, Lecture 1 By Rana Umer
First Generation (1945–55) Vacuum Tubes
• Large and slow
• Engineers design, build, operate and maintain
the computer
• All programming is done with machine
language, or by wiring circuits using cables
• Insert Plugboards into the computer and
operate
• The work is mainly numerical calculations
Intro To OS, Lecture 1 By Rana Umer
First Generation (1945–55) Vacuum Tubes
Intro To OS, Lecture 1 By Rana Umer
2nd Generation (1955–65) Transistors and Batch
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Electronic component transistors introduce in 1950.
Assembly language was used for programming.
Low cost & Small size then First Generation Computer.
Also called mainframes
Computers are managed by professional operators
Punch card used as input (Batch System) (IBM 1401)
For scientific & engineering calculation they were start
using FORTRAN & Assembly languages.
• OS were FMS (Fortran Monitor System)
Intro To OS, Lecture 1 By Rana Umer
2nd: Transistors and Batch Systems
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(a) Programmers bring cards to 1401.
(b)1401 reads batch of jobs onto tape.
(c) Operator carries input tape to IBM 7094 (Real computing).
(d) 7094 does computing.
(e) Operator carries output tape to 1401. (f) 1401 prints output.
Intro To OS, Lecture 1 By Rana Umer
Compiler
Figure 1-4. Structure of a typical FMS job.
Intro To OS, Lecture 1 By Rana Umer
3rd Generation(1965–1980) ICs and Multiprogramming
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IC (Integrated Circuit) Technology was used
Magnetic Disk was used for storage.
High level language used very commonly
Input / Output devices start using.
OS/360: a dinosaur stuck in a tar pit
– Aims to adapts IBM (1401/7904) Functionality, covers all
trades of life (Replaced IBM 1401/7904)
– However, OS/360 introduces several key techniques
• Multi-programming: solve the problem of CPU idling
• Spooling: simultaneous peripheral operation on line
– Whenever a job finishes, OS load a new job from
disk to the empty-partition
Intro To OS, Lecture 1 By Rana Umer
3rd Generation(1965–1980) ICs and Multiprogramming
A multiprogramming system with three jobs in memory.
Intro To OS, Lecture 1 By Rana Umer
3rd Generation(1965–1980) ICs and Multiprogramming
Intro To OS, Lecture 1 By Rana Umer
3rd Generation(1965–1980) ICs and Multiprogramming
• Problems:
– 3rd generation OS was well suited for big scientific
calculations and massive data processing
– Not be able to debug quickly….
Intro To OS, Lecture 1 By Rana Umer
4th Generation(1980–Present) Personal Computers
• Computers have performance similar to 3rd
generation
• Micro Chip was introduced. (Intel Made the chip
in 1971 which was capable to control processing
unit.)
• CP/M(Control Program for Microcomputer)
– First disk-based OS
• 1980, IBM PC, Basic Interpreter, DOS, MS-DOS
• GUI--Lisa—Apple: user friendly
• MS-DOS with GUI– Win95/98/me—winNT/xp…
Intro To OS, Lecture 1 By Rana Umer
5th Generation (Artificial Intelligence)
• Fifth generation computers are in
developmental stage .
• Based on the artificial intelligence.
• The goal of the fifth generation is to
develop the device which could respond
to natural language input and are
capable of learning and self-organization.
• We can say that the fifth
generation computers will have the
power of human intelligence.
Intro To OS, Lecture 1 By Rana Umer
History of Computer Generations
Intro To OS, Lecture 1 By Rana Umer
The Operating Systems
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Mainframe operating systems
(Batch, Transaction & Timesharing Processing)
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Server operating systems
Multiprocessor operating systems
Personal computer operating systems
Handheld operating systems (PDA..)
Embedded operating systems (TV, Mobiles..)
Sensor node operating systems
Real-time operating systems
(Hard & Soft Real-Time Systems)
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Smart card operating systems (Cradit Cards)
Intro To OS, Lecture 1 By Rana Umer
Assignment # 1
• What is an operating system? List some
differences of all Operating Systems?
Intro To OS, Lecture 1 By Rana Umer
Computer Hardware
Some of the components
of a simple personal computer.
Intro To OS, Lecture 1 By Rana Umer
Hardware: Processor
• Brain of computer
– Fetches instruction from memory and execute
– Cycle of CPU:
• fetch, decode, execute
– CPU has General Registers to store variable and
temporary result: load from memory to register;
store from register to memory
– Program counter Register: next instruction
memory address to fetch
– Stack pointer Register: the top of the current stack
Intro To OS, Lecture 1 By Rana Umer
Hardware: Processor
– PSW Register (Program Status Word), priority,
mode…
– The program status word (PSW) is 32 bits in length
and contains the information required for proper
program execution.
– The PSW includes the instruction address,
condition code, and other fields. In general, the
PSW is used to control instruction sequencing and
to hold and indicate the status of the system in
relation to the program currently being executed.
Intro To OS, Lecture 1 By Rana Umer
CPU Pipeline
• Accelerate the execution
(a) A three-stage pipeline. (b) A superscalar CPU.
Intro To OS, Lecture 1 By Rana Umer
Memory
A typical memory hierarchy.
The numbers are very rough approximations.
Intro To OS, Lecture 1 By Rana Umer
Memory
• Memory is where computer fetch and store data,
ideally, it should be both chip/Registers
• The best people can do, is to construct a memory
hierarchy
Registers
• The top layer consists of the registers internal to the
CPU. They are made of the same material as the CPU
and are thus just as fast as the CPU.
• The storage capacity available in them is typically 32 x
32-bits on a 32-bit CPU and 64 x 64-bits on a 64-bit
CPU. Less than 1 KB in both cases.
• Programsmust manage the registers (i.e., decide what
to keep in them) themselves, in software.
Intro To OS, Lecture 1 By Rana Umer
Memory
• Cache lines:
– Memory divided into cache lines
• Cache hit (reports the number of times that a
needed page was found in the data cache)
• Cache misses( reports the number of times
that a needed page was not found in the
cache and had to be read from disk )
– Cache: whenever there is disparity in usage or
speed; used to improve performance
Intro To OS, Lecture 1 By Rana Umer
Memory
• Main memory comes next. This is the
workhorse of the memory system. Main
memory is often called RAM (Random Access
Memory).
• All CPU requests that cannot be satisfied out
of the cache go to main memory.
Intro To OS, Lecture 1 By Rana Umer
Memory
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Next in the hierarchy is Magnetic Disk (Hard Disk).
Cheap and larger than RAM
Slower than RAM
Mechanical movement to fetch data
One or more platter—rotate– rpm
Information is stored on concentric circles
Arm, track, cylinder, sector
Disk helps to implement Virtual Memory
– When no enough memory is available, disks are used
as the storage, and memory as cache
Intro To OS, Lecture 1 By Rana Umer
Memory
• Disk platters are formatted in a system of
concentric circles, or rings, called tracks.
• Within each track are sectors, which subdivide
the circle into a system of arcs, each formatted to
hold the same amount of data—typically 512
bytes.
• Cylinders are the system of identical tracks on
multiple platters within the drive. The multiple
arms of a drive move together in lockstep,
positioning the heads in the same relative
location on all platters simultaneously.
Intro To OS, Lecture 1 By Rana Umer
Hard Disks
Structure of a disk drive.
Intro To OS, Lecture 1 By Rana Umer
Memory
The final layer in the memory hierarchy is Magnetic
Tape.
• This medium is often used as a backup for disk
storage and for holding very large data sets.
• To access a tape, we must have tape reader
• Then the tape may have to be spooled forwarded to
get to the requested block.
• The big plus of tape is that it is exceedingly cheap
per bit and removable, which is important for
backup tapes that must be stored off-site in order to
survive fires, floods, earthquakes , etc.
Intro To OS, Lecture 1 By Rana Umer
Memory
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
I/O devices can be roughly categorized as
• Storage
• Communications
• User-interface, and other
• Devices communicate with the computer via
signals sent over wires or through the air
(Wireless).
• Devices connect with the computer via ports, e.g.
a serial or parallel port.
• A common set of wires connecting multiple
devices is termed a bus.
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
• I/O devices generally consist of two parts:
• Controller
• The Device itself
• Controller
The controller is a chip or a set of chips on a
plug-in board that physically controls the device. It
accepts commands from the operating system.
The software that talks to a controller, giving it
commands and accepting responses, is called a
Device Driver.
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
Input and output can be done in three different ways.
• Simplest method, a user program issues a System Call.
• System Call, Call the kernel then translates into a
procedure call to the appropriate driver.
• The driver then starts the I/O and sits in a tight loop
continuously polling the device to see if it is done
• When the I/O has completed, the driver puts the data
where they are needed (if any), and returns .
• The operating system then returns control to the caller.
• This method is called busy waiting and has the
disadvantage of tying up the CPU polling the device until it
is finished.
CPU Involve
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
• The second method is for the driver to start the
device and ask it to give an interrupt when it is
finished.
• At that point the driver returns. The operating
system then blocks the caller if need be and looks
for other work to do.
• When the controller detects the end of the
transfer, it generates an interrupt to signal
completion.
Interrupts are very important in operating systems
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
• The third method for doing I/O makes use of a
special DMA (Direct Memory Access) special
processor.
• Chip that can control the flow of bits between
memory and some controller without constant
CPU involvement.
• The CPU sets up the DMA chip
• How many bytes to transfer.
• The device and memory addresses involved.
• The direction and lets it go.
• When the DMA chip is done, it causes an
interrupt.
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
• For devices that transfer large quantities of data ( such as disk
controllers ), it is wasteful to tie up the CPU transferring data in
and out of registers one byte at a time.
• Instead this work can be off-loaded to a special processor,
known as the Direct Memory Access, DMA, Controller.
• The DMA controller handles the data transfer, and then
interrupts the CPU when the transfer is complete.
• A simple DMA controller is a standard component in modern
PCs, and many bus-mastering (The bus master is the
program which is the "master" and the I/O devices on the
bus are the "slaves." The bus master actually a program
which controls the bus paths on which the address and control
signals flow.) I/O cards contain their own DMA hardware.
• Handshaking between DMA controllers and their devices is
accomplished through two wires called the DMA-request and
DMA-acknowledge wires.
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
• A common set of wires connecting multiple devices is termed
a bus.
Buses include rigid protocols for the types of messages that
can be sent across the bus and the procedures for
resolving contention issues
System have two types of Buses
• Internal bus ( local bus )
• External bus ( Expansion Bus )
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Intro To OS, Lecture 1 By Rana Umer
I/O Devices
Internal bus (local bus)
• Internal bus, also known as internal data bus, memory bus
or system bus or front-Side-Bus, connects all the internal
components of a computer, such as CPU and memory, to
the motherboard.
• This bus is typically rather quick and is independent of the
rest of the computer operations.
Intro To OS, Lecture 1 By Rana Umer
I/O Devices
External bus ( Expansion Bus)
The external bus connect the different external devices, such
as printer, mouse, keyboard etc., to the computer.
Intro To OS, Lecture 1 By Rana Umer
Booting the Computer
• BIOS—basic input/output system
– On the Motherboard, low-level I/O software
– Checks RAM, keyboard and other basic devices
– Determine the boot device: floppy, CD-ROM, disk
– First sector of the boot-device is read into
memory
– The sector contains program to check which Disk
partition is active
– Then a secondary boot-loader is read into
memory and reads in operating system from the
active Disk partition
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
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Processes
Deadlocks
Memory Management
Input / Output
Files
Security
The shell
Recycling of Concepts
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Processes
• A key concept in all operating systems is the
process.
• A process is basically a program in execution.
• Associated with each process is its address
space, a list of memory
– Other resources like: registers, files, alarms,
related processes, and other information
– A process is fundamentally a container that holds
information for a program to run
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
DeadLocks
• A Deadlock occurs when two or more tasks
permanently block each other by each task
having a lock on a resource which the other
tasks are trying to lock.
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Memory Management
• Memory management is the process of
controlling and coordinating computer memory,
assigning portions called blocks to various
running programs to optimize overall system
performance.
• Memory management resides in hardware, in
the OS (operating system), and in programs
and applications.
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Input / Output
• All computers have physical devices for acquiring
input and producing output.
• Every operating system has an I/O subsystem for
managing its I/O devices.
• Some of the I/O software is device independent,
means, applies to many or all I/O devices equally
well.
• Other parts of it, such as device drivers, are
specific to particular I/O devices.
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Files
• Another key concept supported by virtually all operating
systems is the file system.
• Major function of the operating system is to hide the
peculiarities (unusual characteristic) of the disks and
other I/O devices and present the programmer with a
nice, clean abstract model of device-independent files.
• System calls are obviously needed to create files,
remove files, read files, and write files. Before a file can
be read, it must be located on the disk and opened, and
after it has been read it should be closed, so calls are
provided to do these things.
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Files
Before mounting, the files on the CD-ROM are not accessible
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Security
• Computers contain large amounts of information that
users often want to keep confidential.
• This information may include electronic mail, business
plans, tax returns, and much more.
• It is up to the operating system to manage the system
security so that files, for example, are only accessible to
authorized users.
Intro To OS, Lecture 1 By Rana Umer
Operating System Concepts
Shell
• The shell has the terminal as standard input and
standard output. It starts out by typing the prompt, a
character
OR
• A shell is software that provides an interface for users of
an operating system to access the services of a kernel
Intro To OS, Lecture 1 By Rana Umer
Multiprogramming
• Multiprogramming is a elementary form of parallel
processing in which several programs are run at the
same time on a uniprocessor.
• The operating system executes part of one program,
then part of another, and so on. To the user it appears
that all programs are executing at the same time.
Intro To OS, Lecture 1 By Rana Umer
Memory Protection
• Memory protection is a way to control
memory access rights on a computer, and is a
part of most modern operating systems.
• The main purpose of memory protection is to
prevent a process from accessing memory
that has not been allocated to it
Intro To OS, Lecture 1 By Rana Umer
Multitasking
• The ability to execute more than one task at the
same time, a task being a program.
• The terms multitasking and multiprocessing are
often used interchangeably,
although multiprocessing implies that more than
one CPU is involved.
• In multitasking, only one CPU is involved, but it
switches from one program to another so quickly
that it gives the appearance of executing all of the
programs at the same time.
Intro To OS, Lecture 1 By Rana Umer
Multitasking
• There are two basic types
• Preemptive
• Cooperative.
• In Preemptive Multitasking, the operating
system parcels out CPU time slices to each
program.
• In Cooperative Multitasking, each program can
control the CPU for as long as it needs it. If a
program is not using the CPU, however, it can
allow another program to use it temporarily.
Intro To OS, Lecture 1 By Rana Umer
Timesharing
• Time sharing operating system is a operating system in which
available CPU time is divided into equal slots.
• These slots are assigned to all the users connected to the system.
any user can use the system only for the specified time slot. if he
finishes his work within the given time slot, that's fine but if he still
got some work pending then he will again wait for his turn to
complete the remaining work.
• The time slots of CPU are distributes to all the connected users in
first come first serve basis and then their turn comes in round robin
fashion.
• Time sharing operating system are used when a powerful server
computer serves several client computers.
Intro To OS, Lecture 1 By Rana Umer
System Calls
• Operating systems contain sets of routines for performing
various low-level operations.
• If you want to execute an operating system routine from
a program, you must make a system call.(System Call not only
transfer the control but it transfer the privileges)
• The interface between the operating system and the user
programs is defined by the set of system calls that the
operating system provides.
• The system calls available in the interface vary from OS to
OS (What & How to do) (although the underlying concepts
tend to be similar).
• Only System Calls enter the kernel and Procedure Calls do
not
Intro To OS, Lecture 1 By Rana Umer
System Calls
System Calls could be….
• System Calls for Process Management
• System Calls for file Management
• System Calls for Directory Management
• Miscellaneous System Calls (Change the name of file/Directory etc.)
• The Windows Win32 API (Application Program Interface)
Process Status Word Register (PSW)
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
It is time to take a look inside…
• They give an idea of some designs that have been tried in
practice.
• In order to get some idea of the spectrum of possibilities
The Five Designs Approaches we discuss here
1. Monolithic Systems
2. layered Systems
3. Virtual Machines
4. Exokernels
5. Client-Server Systems.
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Monolithic Systems (Procedure System)-- “The BigMess.”
• Monolithic architecture, in which functionally
distinguishable aspects are not architecturally separate
components but are all interwoven.
• The operating system is written as a collection of
procedures, each of which can call any of the other ones
whenever it needs to.
• This technique is used interface in terms of parameters
and results, and each one is free to call any other one.
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Monolithic Systems Basic Structure is…
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A Main Program that invokes the requested service
procedure.
A Set Of Service procedures that carry out the system
calls.
A Set Of Utility procedures that help the service
procedures.
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Monolithic Systems Basic Structure is…
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Layered Systems (Batch System)
• In this approach organize the operating system as a
hierarchy of six layers. (Netherland 1968)
( System Operator )
( Application )
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Virtual Machine
The virtual machine typically emulates a physical computing
environment, but requests for CPU, memory, hard disk, network and
other hardware resources are managed by a virtualization layer which
translates these requests to the underlying physical hardware.
• OS/360 (Problem is multiuser)
• VM (often: VM/CMS) is a family of IBM virtual machine operating
systems used on IBM mainframes System/370, System/390 ..etc
• The first version, released in 1972, was VM/370, or officially Virtual
Machine Facility/370.
• So on till date…..
• JVM (Java Virtual Machine). The Java compiler produces code for
JVM, which then typically is executed by a software JVM interpreter
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Exokernels
• Going one step further, researchers have built a system that gives
each user a clone of the actual computer, but with a subset of the
resources (Thus one virtual machine might get disk blocks 0 to
1023, the next one might get blocks 1024 to 2047, and so on.)
• At the bottom layer, running in kernel mode, is a program called the
exokernel.
– Its job is to allocate resources to virtual machines and then
check attempts to use them to make sure no machine is trying to
use somebody else’s resources.
– Each user-level virtual machine can run its own operating
system, except that each one is restricted to using only the
resources.
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Exokernels
– With the exokernel, Virtual machine monitor maintain tables
remapping is not needed.
– The exokernel need only keep track of which virtual machine has
been assigned which resource.
Intro To OS, Lecture 1 By Rana Umer
OS Structure (Inside)
Client Server Model
• To request a service, sends the request to a server
process, which then does the work and sends back the
answer.
Intro To OS, Lecture 1 By Rana Umer