1. Miss Maheen Sadiq
Under the guideline of
Sir Syed Rizwan-ul-Hasan
Assistant Professor
CED, SSUET

2. Introduction (Week 1)

3. What is Operating System?
 An operating system is a layer of software which takes care of
technical aspects of a computer's operation.
 Examples: Windows, Linux, Unix and Mac OS, etc.,

4. Function of Operating System
 Resource management
-Time management (CPU and Disk Scheduling)
-Space management(main and secondary storages)
-Process synchronization and deadlock handling.
-Accounting and status information
 User friendliness
-Execution environment
-Error detection and handling
-Protection and security
-Fault tolerance and failure recovery

5. Types of Advanced Operating System
 It can be categorized on the following basis of
- Architecture Driven
• A variety of high speed architecture
• Extremely fast parallel
• Offers great potential for speed up
Distributed Operating Systems
Multiprocessor Operating Systems
- Application Driven
• Require special operating system support as a requirement as well as
for efficiency.
Database Operating Systems
Real-time Operating Systems

6. Types of Advanced Operating System
Advanced Operating Systems
Architecture Driven
Application Driven
Distributed Multiprocessor Database Systems Real-time
Systems systems Systems

7. Distributed Systems
 They are for network of autonomous computers connected by a
communication network.
 It controls and manages the h/wand s/w resources of a DS such
that its users view the entire system as a power full monolithic
computer system.
 However, design is much more complex due to the lack of both
shared memory and common clock and unpredictable
communication delays.
 Basic issues are same as traditional OS
• Advantages of DS
– Resources Sharing
– Computation speed up – load sharing
– Reliability
– Communications

8. Multiprocessor Operating System
 Consists of a set of processors that
 share a set of physical memory blocks
 share a common clock
 "share" over an interconnection network.
 Control and manage resources
 hardware and software resources
 viewed as a uniprocessor system.
 Design issues same as traditional system.
 Practical issues:
 increased complexity of synchronization, scheduling, memory
management, protection and security.

9. Database Operating System
 Database systems place increased demands on an operating
system to efficiently support:
 concept of a transactions
 manage large volumes of data
 concurrency control
 system failure control
 Should also have buffer management schemes for data
retrieval and storage from secondary storage
 Concurrency control is one of the most challenging
problems in the design of database operating systems

10. Real-time Operating Systems
 Systems where jobs have completion deadlines
 In soft real-time systems, jobs should be completed before its
deadline to be of use
 In hard real-time systems, jobs should be completed before its
deadline to avert a disaster
 Jobs should be scheduled in such a way that a maximum
number of jobs satisfy their deadlines
 Requirements can vary from application to application

11.  Network Operating System
 A network operating system (NOS) is a computer operating
system that is designed primarily to support
workstation, personal computer, and, in some
instances, older terminal that are connected on a local area
network (LAN).
 A network operating system provides printer
sharing, common file system and database
sharing, application sharing, and the ability to manage a
network name directory, security, and other housekeeping
aspects of a network.

12. Architecture of Distributed
System (Week 2)

13. Architecture of Distributed System
 A distributed system is a collection of autonomous computers
which do not share memory or a clock
 Computers communicate with each other by exchanging
messages over a communication network
 Each computer has its own memory and runs its own OS
 Resources owned and controlled by a computer are said to be
local to it
 Resources owned and controlled by other computers are said to
be remote

14. Architecture of Distributed System
 Accessing remote resources is more expensive because of
communication delays
 Motive is to convert low cost microprocessors to single
powerful system

15.  Advantages
 Resource sharing
 Hardware and software resources can be shared
 Printer, Compiler, Text Editors, Databases, etc.
 Enhanced performance
 Rapid response time
 Higher system throughput
 Many tasks can be concurrently executed at different
computers
 Distributed system can employ load distribution techniques
 Tasks at heavily loaded systems are transferred to lightly
loaded computers
 Waiting time of a task can be reduced

16.  Improved reliability and availability
 Few components of the system can fail without affecting the
availability
 System can be made fault tolerant through replication of data
and services
 Data can be files and directories and services can be the
processes that
 provide functionality
 Modular expandability
 New hardware and software can be easily added without
replacing the existing system
 Disadvantages
 Complexity
 Security
 Manageability
 Unpredictability

17. Architecture of Distributed System
CPU
CPU
Disk
Memory
Memory
Communication
Network
CPU CPU
Disk Disk
CPU Memory
Memory
Memory

18.  Architecture types
DS can be classified into three broad categories:
 Minicomputer model
 Workstation model
 Processor pool model
Minicomputer Model
 DS consists of several minicomputers
 e.g. VAX processors
 Each machine supports multiple users and share resources
 Ratio between no. of processors to no. of users is usually
less than one

19. Workstation Model
 Consists of several workstations ( up to several thousands)
 Each user has a workstation at his disposal, which consist
of powerful processor, memory and display
 With the help of DFS, users can access data regardless of
its location
 Ratio between no. of processors to no. of users is usually 1
 e.g. SSUET WS1 (Workstation1) and user1

20. Processor Pool Model
 Ratio between processor to no. of users is normally greater
than 1
 This model allocates one or more processors according to
users’ need
 Once the processors complete their jobs, they return to the
pool and await a new assignment
 Amoeba is a combination of the processor pool model and
workstation model

21.  Issues in Distributed Operating System
Important Issues in the design of a distributed operating
system
 Global knowledge
 Naming
 Scalability
 Compatibility
 Process Synchronization
 Resource Management
 Security
 Structuring
 Client-Server Computing Model

22.  Global Knowledge
 In case of shared memory systems ,up-to date state of all
processes and resources of the system is completely known
 Whereas in distributed system it is much complex
 Up-to date state of all processes and resources can not be
known because of absence of shared memory and clock and
unexpected delays
 Fundamental problems in the design of DOS is to determine
efficient technique to implement decentralized system wide
control
 Another problem is to how to order all the events that occur
on different times at different computers in the absence of
global clock

23.  Naming
• Names are used to refer to objects
• Computers, printers, services, files and users
• Eg. Name service maps a logical name into a physical
address, by using table lookup or by algorithm
• If an algorithm is used for mapping, the algorithm would
depend upon the structure of the names
• Another issues in naming is the method of naming objects
such that an object can be located irrespective of its logical
name

24.  Scalability
• Systems generally grow with time
• Design should be such that system should not result in
system unavailability or degraded performance when
growth occurs
 E.g. broadcast based protocols work well for small systems
but not for large systems
 Distributed File System

25.  Compatibility
• Refers to the interoperability among the resources in a system
• There are three levels of compatibility in DS
• Binary Level: all processes execute the same instruction set
even though the processors may differ in performance and in
input-output
• E.g. Emerald distributed system
• Program development is easy
• DS cannot include computers with different architectures
• Rarely supported in large distributed systems

26.  Process Synchronization
• Process synchronization is difficult because of unavailability of
shared memory
• DOS has to synchronize process running at different computers
when they try to concurrently access shared resources
• Mutual exclusion problem
• Request must be serialized to secure the integrity of the shared
resources
• In DS, process can request resources (local or remote) and
release resources in any order
• If the sequence of the resource allocation is not
controlled, deadlock may occur which can lead to decrease in
system performance

27.  Resource Management
• Concerned with making both local and remote resources
available to users in an effective manner
• Users should be able to access remote resources as easily as they
can access local resources
• Specific location of resources should be hidden from users in the
following ways:
 Data Migration
 Computation Migration and
 Distributed scheduling

28.  Data Migration
• Data can either be file or contents of physical memory
• In process of data migration, data is brought to the location of
the computation that needs access to it by the DOS
• If computation updates a set of data, original location may have
to be updated
• In case of file DFS is involved
• DFS is a component of DOS that implements a common file
system available to the autonomous computers in the system
• Primary goal is to provide same functional capability to access
files regardless of their location
• If the data accessed is in the physical memory of another system
then a computation’s data request is handled by distributed
shared memory

29.  Computation Migration
• In computation migration, computation migrates to another
location
• It may be efficient when information is needed concerning a
remote file directory
• it is more efficient to send the message and receive the
information back, instead of transferring the whole directory
• Remote procedural call has been commonly used for
computation migration
• Only a part of computation of a process is normally carried out
on a different machine

30.  Security
 OS is responsible for the security of the computer system
 Two issues must be considered:
 Authentication: process of guaranteeing that an entity is what
it claims to be
 Authorization: process of deciding what privileges an entity
has and making only these privileges available

31. Communications Network
(Week 3)

32.  Communication Networks
 Computers in a DS are interconnected through a computer
communication network
 Computer can exchange messages with other computers and
access data stored at another computer through this network
 Layered protocols are commonly used for communication
purpose

33.  Wide-Area Networks
• WANs consist of switches that are usually interconnected by communication
links.
• Data is transferred b/w computers through a series of switches called point-
to-point.
• A path may become congested due to heavy data communication through
path or limited bandwidth.
• The data can be lost due to switch crashes, communication link failure,
limited buffer capacity at switch, transmission error, etc

34.  Packet Switching Vs. Circuit Switching
 Circuit Switching:
 A dedicated path is established b/w two devices wishing to
communicate, and the path remains intact for the entire
transmission.
 The telephone system uses circuit switching.
 The path is broken when one side terminate the connection.
• Packet Switching:
 A connection is established be/w the source device and its
nearest switch.
 These packets are routes from one switch to another until
they arrive at the switch connected to the destination device.
 Parallel transmission possible.
 The breaking of a message into packets & assembling them
back at the destination carries some cost.

35. Layered Protocols
ISO OSI Reference Model

36.  The OSI Model
• A widely accepted structuring technique is layering
• The communications functions are partitioned into a hierarchical
set of layers
• Each layer performs a related subset of the functions required to
communicate with another system
• The resulting OSI architecture has seven layers
 Physical layer:
 The physical layer is responsible for handling both
the mechanical and electrical details of the physical
transmission of a bit stream
 This layer is implemented in the hardware of the
network device.

37.  Network layer:
 The network layer is responsible for providing connections
and for routing packets in the communication network
 includes handling the address of outgoing packets, decoding
the address of incoming packets, and maintaining routing
information for proper response to changing load levels.
 Transport layer:
 The transport layer is responsible for two level accesses to
the network and for transfer of messages between the
clients
 includes partitioning the messages into packets, maintaining
packet order, controlling flow, and generating physical
addresses

38.  Session layer:
 Session layer is responsible for implementing sessions, or
process to process communications protocols
 Typically these protocols are the actual communications for
remote logins and for file and mail transfers.
 Presentation layer:
 Presentation layer performs transformations on data to
provide a standardization application interface and provide
common communications services;
 examples encryption, text compression, reformatting
 Application layer:
 The application layer is responsible for interacting directly
with the users
 This layer deals with file transfer, remote login protocol,
and electronic mail.

39.  Local-Area Networks
• LAN is a communication network that interconnects a variety of
data communication devices with in a small graphical area.
• High data transmission rate 10MB to100MB per second.
• The graphical scope is small & for single building.
• Low transmission error.

40.  CSMA/CD Protocol
 Most commonly used access control protocol for bus topology.
 A device wishing to transmit listen to the medium to determine
whether another transmission is in progress.
 The advantage of this protocol is simplicity.
 The disadvantage is under a heavy load, contention for the bus
rises and performance degrades because of frequent collision.
 It cannot support a large number of devices per bus.
 Example: Ethernet

41.  Token Bus Protocol
• Devices physically organized in a tree/bus topology form a logical
ring, each device knows the identity of the devices proceeding and
the following it on the ring.
• Access to the bus is controlled through a token.
• The device holding the token its allowed to transmit.
• A device is allowed to keep the to keep the token for a specific
amount of duration.

42.  Ring Topology
• The ring topology is much like the bus in that each workstation
and file server is attached to a central cable
• the workstations and file server are connected together to form a
ring
• The workstations and file servers take turns passing information
from one to another until the information reaches its final
destination

43.  Communication Primitives
• Communication primitives are the high level construct with
which programs uses the underlying communication network.
• The designer of a communication network must address four
basic issues:
• Naming and Name Resolution: How do two processes locate
each other to communicate?
• Routing Strategies: How are messages sent through the
network?
• Packet Strategies: Are packets sent individually or as a
sequence?
• Connection Strategies: How do two processes send a
sequence of messages?
• Contention: The network is a shared resource, so how do we
resolve conflicting demands for its use?

44.  Message Passing Model
• Has two basic communication primitives, namely SEND and
RECEIVE.
• SEND primitive has two parameters, a message and its destination.
• RECEIVE primitive has two parameters, the source of the message
and buffer for storing the message
• An application of these primitives can be found in the client-server
computational model.
• A client process needing some service sends a message to the server
and waits for a reply message.

45.  Blocking Vs. Non Blocking Primitive
 Non Blocking Primitives:
• The SEND primitive returns control to the user process as soon as the
message is copied from the user buffer onto the kernel buffer.
• The corresponding RECEIVE primitive signals its intention to receive a
message and provides a buffer to copy for the arrival of a message.
• Program have maximum flexibility to perform computation and
communication in any order they want
• Programming becomes tricky and difficult.
 Blocking Primitives
• The SEND primitive does not return control to the user program until the
message has been sent or until an acknowledgement has been received
• RECEIVE primitive does not return control until a message is copied to the
user buffer.
• Behavior of the programs predictable & programming is relatively easy.
• The lack of flexibility in programming & the absence of concurrency b/w
computation and communication.

46.  Synchronization Vs. A synchronization Primitives
 Synchronization :
• SEND primitives is blocked until a corresponding RECEIVE primitive is
executed at the receiving computer
• This strategy is also referred to as a rendezvous.
 A synchronization
• SEND primitive does not block even if there is no corresponding
execution of a RECEIVER primitive.
• The corresponding RECEIVE primitive can either be a blocking or a no
blocking primitive.
• Buffering message is more complex.

47. Communication: remote
Procedure Calls
(Week:4)

48.  Remote Procedural Call
 A More natural way to communicate is through Procedural call:
 every language supports it .
 semantics are well defined and understood .
 natural for programmers to use.
 Programmer Using such a model must handle the following
details:
 Pairing of responses with request messages.
 Data representation.
 Knowing the address of remote machine on the server
 Taking care of communication and system failure

49. RPC

50.  Basic RPC Operation
• The RPC Mechanism is based on the observation that a procedural call
is well known for transfer of control and data with in a program running
an a single machine.
• On invoking a remote procedure, the calling process is suspended.
• If any parameter are passed to the remote machine where the procedure
will execute.
• On completion, the result are passed back from server to client and
resuming execution as if it had called a local procedure.
• RPC mechanism is based on the concept of stub procedures.
• The server writer writes the server and links it with the server-side
stubs; the client writes her program and links it with the client-side
stub.
• The stubs are responsible for managing all details of the remote
communication between client and server.

51.  Design Issues in RPC
• RPC mechanism is based on the concept of stub procedures.
• The server writer writes the server and links it with the
server-side stubs; the client writes her program and links it
with the client-side stub.
• The stubs are responsible for managing all details of the
remote communication between client and server.

52.  Design Issues

53.  Binding
• Binding is process that determines the remote procedure, and the
machine on which it will be executed.
• It may also check the compatibility of parameters passed and
procedure type called.
• Binding server essentially store the server machine along with the
services they provide.
• Another approach used for binding is where the client specifies the
machine and the service required and the binding server returns the
port number for communication.

54. Parameter and Result