operating system basic concepts

1. OPERATING SYSTEMS
S5R
Name of Faculty: Reena Murali
Dept. of Computer science
RIT

2. Introduction and Overview
What is an operating system?
How have operating systems evolved?
Why study operating systems?

3. What is an Operating System?
• Not easy to define precisely…
Users
Applications
Operating System
Hardware
• OS:
compilers
databases
word processors
CPU
memory
I/O devices
Everything in system that isn’t an application or hardware
• OS:
Software that converts hardware into a useful form for
applications

4. What is the role of the OS?
• Role #1: Resources provider
•
What is a resource?
– Anything valuable (e.g., CPU, memory, disk)

5. What is the role of the OS?
• Role #2: Resource coordinator (I.e.,
manager)
• Advantages of resource coordinator
– Virtualize resources so multiple users or
applications can share
– Protect applications from one another
– Provide efficient and fair access to resources

6. What Functionality belongs in
OS?
• No single right answer
• Desired functionality depends on outside
factors
– OS must adapt to both user expectations
and technology changes

7. OS Concepts

8. A Computer System:

9. • OS can be viewed as
Users
Applications
Operating System
Hardware
compilers
databases
word processors
CPU
memory
I/O devices

10. OPERATING
SYSTEM OVERVIEW
Humans
Program Interface
User Programs
O.S. Interface
O.S.
Hardware Interface/
Privileged Instructions
Disk/Tape/Memory
The Layers Of
A System

11. Conclusion

12. An Operating system is
• An interface between users and hardware
- an environment "architecture”
• Allows convenient and efficient usage of
resources (Gives each user a slice of the
resources)
• Provides information protection
• Acts as a control program.

13. Example OS

14. Common Operating Systems
• DOS
• Windows 95,98,2000, NT, XP, Vista …
• UNIX / LINUX (Distributions like Red Hat,
Suse, Debian, Ubuntu…. ), MacOS

15. Evolution of OS

16. Evolution of Operating Systems
•
•
•
•
•
•
•
•
Early Systems (1950)
Simple Batch Systems (1960)
Multiprogrammed Batch Systems (1970)
Time-Sharing (1970)
Personal/Desktop Systems (1980)
Multiprocessor Systems (1980)
Networked/Distributed Systems (1980)
Real-Time (1970) and Handheld (1990)

17. Batch Processing
Batch: Group of jobs submitted together
– Operator collects jobs; orders efficiently; runs one at a
time
• Advantages
– Keep machine busy while programmer thinks
– Improves throughput and utilization
• Disadvantages
– User must wait until batch is done for results
– Machine idle when job is reading from cards and
writing to printers

18. Multiprogrammed Systems
• Goal of OS
– Improve performance by always running a job
– Keep multiple jobs resident in memory
– When job waits for disk I/O, OS switches to another
job
• OS Functionality
– Job scheduling policies
– Memory management and protection
• Advantage: Improves throughput and utilization
• Disadvantage: Machine not interactive

19. Interactive Multiprogramming

20. Time Sharing Systems (TSS)
• Batch multiprogramming does not support
interaction with users.
• In time sharing systems multiple users
simultaneously access the system through
terminals .
• Processor’s time is shared among multiple
users.

21. Why does Time-Sharing
work?
• Because of slow human reaction time, a
typical user needs 2 seconds of
processing time per minute.
• Then many users should be able to share
the same system without noticeable delay
in the computer reaction time.
• The user should get a good response
time.

22. Personal/Desktop Systems
• Personal computers –
dedicated to a single user.
computer
system
• I/O devices – keyboards, mice, display screens,
small printers.
• May run several different types of operating
systems (Windows, MacOS, UNIX, Linux)

23. Other Systems
• Multi User Systems
• Multi Tasking Systems

24. Networked Systems
• Requires networking infrastructure.
• Local area networks (LAN) or Wide
area networks (WAN).
• May be either Centralized Sever or
Client-Server or Peer-to-Peer (P2P)
systems.

25. Local Area Network (LAN) structure

26. Wide Area Network (WAN) structure

27. Client/Server Environment

28. Client-Sever Systems

29. Peer-To-Peer (P2P) Systems

30. •
**Networked/Distributed
Systems computation
Distribute resources and the
among several physical processors.
• Loosely coupled system:
– each processor has its own local memory.
– processors communicate with one another
through various communications lines.
• Advantages:
– Resources Sharing
– Computation speed up – load sharing
– Reliability

31. Networked/Distributed System
Structure
node 1
node 2
disk
disk
processors
processors
disk
disk
network
node 3
node N
disk
disk
processors
processors
disk
…
disk

32. Networked/Distributed Operating
Systems
• Network Operating System (NOS):
– provides mainly file sharing.
– Each computer runs independently from other
computers on the network.
• Distributed Operating System (DOS):
– gives the impression there is a single operating
system controlling the network.
– network is mostly transparent – it’s a powerful
virtual machine.

33. Real-Time Systems (RTS)
• Note that not all Operating Systems are
general-purpose systems.
• Real-Time (RT) systems are dedicated
systems that need to adhere to deadlines ,
i.e., time constraints.
• Correctness of the computation depends
not only on the logical result but also on
the time at which the results are produced.

34. Hard Real-Time Systems
• Hard real-time system:
– Must meet its deadline.
• Often used as a control device in a dedicated
application:
– Industrial control
– Robotics
• Secondary storage limited or absent, data stored
in short term memory, or read-only memory
(ROM).

35. Soft Real-Time Systems
• Soft real-time system:
– Deadline desirable but not mandatory.
– Limited utility in industrial control or
robotics.
– Useful in modern applications
(multimedia, virtual reality) requiring
advanced operating-system features.

36. Handheld Systems
• Handheld systems are also dedicated.
– Personal Digital Assistants (PDAs).
– Cellular telephones.
• Issues:
– Limited memory
– Slow processors
– Small display screens
– Support for multimedia (images, video)

37. Migration of OS Concepts and
Features

38. Operating-System Concepts
•
•
•
•
functions of OS
Operating System Services
System Calls
OS Structure

39. Functions of OS
•
•
•
•
•
•
•
•
Process Management
Main Memory Management
File Management
I/O System Management
Secondary Management
Networking
Protection System
Command-Interpreter System

40. Process Management
• A process is a program in execution. A process
needs certain resources, including CPU time,
memory, files, and I/O devices, to accomplish
its task.
• The operating system is responsible for the
following activities in connection with process
management.
– Process creation and deletion.
– process suspension and resumption.
– Provision of mechanisms for:
• process synchronization
• process communication

41. Main-Memory Management
• Memory is a large array of words or bytes, each with its
own address. It is a repository of quickly accessible data
shared by the CPU and I/O devices.
• Main memory is a volatile storage device. It loses its
contents in the case of system failure.
• The operating system is responsible for the following
activities in connections with memory management:
– Keep track of which parts of memory are currently
being used and by whom.
– Decide which processes to load when memory space
becomes available.
– Allocate and deallocate memory space as needed.

42. File Management
• A file is a collection of related information defined by its creator.
Commonly, files represent programs (both source and object forms)
and data.
• The operating system is responsible for the following activities in
connections with file management:
– File creation and deletion.
– Directory creation and deletion.
– Mapping files onto secondary storage.
– File backup on stable (nonvolatile) storage media.

43. I/O System Management
• The I/O system consists of:
– A buffer-caching system
– A general device-driver interface
– Drivers for specific hardware devices

44. Secondary-Storage
Management
• Since main memory (primary storage) is volatile and too
small to accommodate all data and programs
permanently, the computer system must provide
secondary storage to back up main memory.
• Most modern computer systems use disks as the
principle on-line storage medium, for both programs and
data.
• The operating system is responsible for the following
activities in connection with disk management:
– Free space management
– Storage allocation
– Disk scheduling

45. Networking (Distributed Systems)
• A distributed system is a collection processors that do not share
memory or a clock. Each processor has its own local memory.
• The processors in the system are connected through a
communication network.
• Communication takes place using a protocol.
• A distributed system provides user access to various system
resources.
• Access to a shared resource allows:
– Computation speed-up
– Increased data availability
– Enhanced reliability

46. Protection System
• Protection refers to a mechanism for
controlling
access
by
programs,
processes, or users to both system and
user resources.
• The protection mechanism must:
– distinguish between authorized and
unauthorized usage.
– specify the controls to be imposed.
– provide a means of enforcement.

47. Command-Interpreter System
• Many commands are given to the operating system by control
statements which deal with:
– process creation and management
– I/O handling
– secondary-storage management
– main-memory management
– file-system access
– protection
– networking

48. Command-Interpreter System
(Cont.)
• The program that reads and interprets
control statements is called variously:
– command-line interpreter
– shell (in UNIX)
Its function is to get and execute the next
command statement.

49. Additional Operating System
Functions
Additional functions exist not for helping the user, but rather for
ensuring efficient system operations.
• Resource allocation – allocating resources to multiple
users or multiple jobs running at the same time.
• Accounting – keep track of and record which users
use how much and what kinds of computer resources
for account billing or for accumulating usage statistics.
• Protection – ensuring that all access to system
resources is controlled.

50. OS SERVICES

51. Operating System Services
• Program execution – system capability to load a program
into memory and to run it.
• I/O operations – since user programs cannot execute I/O
operations directly, the operating system must provide
some means to perform I/O.
• File-system manipulation – program capability to read,
write, create, and delete files.
• Communications – exchange of information between
processes executing either on the same computer or on
different systems tied together by a network.
Implemented via shared memory or message passing.
• Error detection – ensure correct computing by detecting
errors in the CPU and memory hardware, in I/O devices,
or in user programs.

52. System Calls

53. System Calls
• System calls provide the interface between a running
program and the operating system.
– Generally available as assembly-language
instructions.
– Languages defined to replace assembly language for
systems programming allow system calls to be made
directly (e.g., C, C++)
• Three general methods are used to pass parameters
between a running program and the operating system.
– Pass parameters in registers.
– Store the parameters in a table in memory, and the
table address is passed as a parameter in a register.
– Push (store) the parameters onto the stack by the
program, and pop off the stack by operating system.

54. Passing of Parameters As A
Table

55. Types of System Calls
•
•
•
•
•
Process control
File management
Device management
Information maintenance
Communications

56. Components of OS

57. The OS Shell
• Defines interface between OS and
users
– Windows GUI
– UNIX command line
– UNIX users can choose among a variety of
shells
• csh is the “C shell”
• tcsh is an enhanced “C shell”

58. OS Shell interface
Users
Users
O/S
shell
Users

59. The OS Kernel
• The internal part of the OS is often
called the kernel
• Kernel Components
– File Manager
– Device Drivers
– Memory Manager
– Scheduler
– Dispatcher

60. OS File Manager
• Maintains information about the
files that are available on the
system
• Where files are located in mass
storage, their size and type and
their protections, what part of
mass storage is available
• Files usually allowed to be
grouped in directories or
folders. Allows hierarchical
organization.

61. OS Device Drivers
• Software to communicate with peripheral
devices or controllers
• Each driver is unique
• Translates general requests into specific
steps for that device

62. OS Memory Manager
• Responsible for coordinating the
use of the machine’s main
memory
• Decides what area of memory is
to be allocated for a program
and its data
• Allocates and deallocates
memory for different programs
and always knows what areas
are free

63. OS Scheduler
• Maintains a record of processes that are
present, adds new processes, removes
completed processes
– memory area(s) assigned
– priority
– state of readiness to execute (ready/wait)

64. OS Dispatcher
• Ensures that processes that are
ready to run are actually
executed
• Time is divided into small (50
ms) segments called a time
slice
• When the time slice is over, the
dispatcher allows scheduler to
update process state for each
process, then selects the next
process to run

65. OS structures

66. Design Approaches
• Three common approaches:
– Kernel Approach
• monolithic kernel
• microkernel
• exokernel
– Layered Approach
– Virtual Machine Approach

67. Kernel approach

68. Kernel Based Approach
•
•
•
•
Kernel contains a collection of primitives which are used to build the OS
OS implements policy, Kernel implements mechanisms
The advantage is performance, the disadvantage are complexity and
maintainability
Why use this approach? If you have a relatively “small” kernel the gains in
performance and efficiency outweigh the disadvantages.
User Applications
User
Apps
Sys
Services
kernel-user interface
kernel-user interface
kernel (privileged)
kernel (privileged)
hw-sw interface
hw-sw interface
hardware
hardware
References:
1. Brinch Hansen, P., "The Nucleus of a Multiprogramming System", Communications of the ACM, Apr. 1970, pp. 238-241.
2. D. Ritchie, and K. Thompson, “The UNIX Time-Sharing System”, Communications of the ACM, Vol. 17, No. 7, Jul. 1974, pp. 365-375.
3. Wulf, W., E. Cohen, W. Corwin, A. Jones, R. Levin, C. Pierson, and F. Pollack, "HYDRA: The Kernel of a Multiprocessor Operating
System", Communications of the ACM, June 1974, pp. 337-345.

69. 1. Monolithic Operating System

70. MS-DOS System Structure
• MS-DOS – written to provide the most
functionality in the least space:
– not divided into modules (monolithic).
– Although MS-DOS has some structure, its
interfaces and levels of functionality are not
well separated.

71. MS-DOS System Structure

72. UNIX System Structure
•
•
UNIX – limited by hardware functionality, the original UNIX OS
had limited structuring.
The UNIX OS consists of two separable parts:
1. Systems Programs:
2. The Kernel:
• Consists of everything below the system-call interface and
above the physical hardware
• Provides the file system, CPU scheduling, memory
management, and other operating-system functions; a
large number of functions for one level.

73. UNIX System Structure

74. Traditional UNIX Kernel [Bach86]

75. 2. Microkernel System Structure (1)
• Move as much functionality as possible from the kernel into “user”
space.
• Only a few essential functions in the kernel
– primitive memory management (address space)
– I/O and interrupt management
– Inter-Process Communication (IPC)
– basic scheduling
• Other OS services are provided by processes running in user mode
(vertical servers) – device drivers, file system, virtual memory…

76. 2. Microkernel System Structure (2)
• Communication takes place between user
modules using message passing.
• But a performance penalty caused by
replacing service calls with message
exchanges between process.
• More flexibility, extensibility, portability and
reliability (details in next 4 slides).

77. Microkernel Operating System

78. Benefits of a Microkernel Organization
(1)
• Extensibility/Reliability
– modular design.
– easy to add services.
– small microkernel can be rigorously tested.
• Portability
– changes needed to port the system to a new
processor is done in the microkernel in the other services.
not

79. Benefits of Microkernel Organization
(2)
• Distributed system support
– message are sent without knowing
what the target machine is.
• Object-oriented operating system
– components are objects with clearly
defined interfaces that can be
interconnected to form software.

80. Mach 3 Microkernel Structure

81. Windows NT Client-Server
Structure

82. Windows NT 4.0 Architecture

83. The Neutrino Microkernel

84. 3. Exokernel
• Takes micro-kernel to the extreme
• Services implemented as user space library linked against
application.
• Only a minimum of functionality is implemented in the kernel,
such as context switching and MMU management.
• Export hardware resources that may be managed by user-level
applications while the kernel implements the protection
mechanism
• Apps may optimize to a given hardware platform or create new
resource abstractions
References:
• D. R. Engler M. F. Kaashoek J. O'Toole, Jr., “Exokernel: an operating system architecture for application-level resource management”,
Proceedings of the fifteenth ACM symposium on Operating systems principles, pp. 251-266, Copper Mountain, Colorado, 1995.

85. Layered Approach

86. Layered Approach
• The operating system is divided into a
number of layers (levels), each built on top
of lower layers. The bottom layer (layer
0), is the hardware; the highest (layer N) is
the user interface.
• With modularity, layers are selected such
that each uses functions (operations) and
services of only lower layers.

87. General OS Layers

88. Layered Operating System

89. Older Windows System Layers

90. OS/2 Layer Structure

91. Layered vs. Microkernel
Architecture

92. Virtual Machine Approach
• Virtual software layer over hardware
• Illusion of multiple instances of hardware
• Supports multiple instances of OSs
VM1
VM2
VM3
VM4
Virtual machine software
Hardware
References:
• Seawright, L., and R. MacKinnon, "VM/370 - A Study of Multiplicity and Usefulness", IBM Systems Journal, 1979, pp. 4-17.

93. Virtual Machines
• A virtual machine takes the layered approach to its logical
conclusion. It treats hardware and the operating system kernel as
though they were all hardware.
• A virtual machine provides an interface identical to the underlying
bare hardware.
• The operating system creates the illusion of multiple processes,
each executing on its own processor with its own (virtual) memory.

94. OS Summary
• Shell -- interface to user
• File Manager -- manages mass
memory
• Device Drivers -- communicate with
peripherals
• Memory Manager -- manages main
memory
• Scheduler & Dispatcher -- manage
processes

95. Different Operating Systems
on the Same Machine ?
• It is possible to have more than one
operating system available to be used
on a machine.
• Only one operating system is run at a
time, though.
• Examples:
– VAX -- VMS or Ultrix
– PCs -- DOS, Windows, or Linux

96. Utilities
• Operating systems usually come with
some associated utility programs
• UNIX usually has the text editors emacs
and vi (and sometimes pico)
• UNIX has its own sort utility
• UNIX has its own mail utility