Operating Systems, Introduction of OS, Objectives of OS, Service provided by the OS, OS as resource manager, Evolution of OS, Simple batch systems, Multi programmed batch systems, Time sharing systems, Major achievements of OS, Process, memory management, information protection and security, scheduling and resource management, System structure of OS, developments leading to modern operating systems, microkernal architecture, multithreading, distributed OS, Symmetric multiprocessing, object oriented design

1. Done by,
Dr. D. Veera Vanitha, AP/ECE,
School of Engineering,
Avinashilingam Institute for Home Science and
Higher Education for Women, Coimbatore.

2.  Convenience - An OS makes a computer
more convenient to use
 Efficiency - An OS allows the computer
system resources to be used in an efficient
manner
 Ability to evolve - An OS should be
constructed in such a way as to permit the
effective development, testing, and
introduction of new system functions without
interfering with service.

3.  Program development
 Program execution
 Access I/O devices
 Controlled access to files
 System access
 Error detection and response
 Accounting

4. A computer is a set of resources for moving, storing, &
processing data
 The OS is responsible for managing these resources

5. - A major OS will evolve over time for a number
of reasons. They are:
 Hardware upgrades plus new types of hardware
 New services
 Fixes

6. Key requirement for an OS includes:
 Serial processing
- No operating system
- Machines run from a console with display lights,
toggle switches, input device, and printer
Problems are:
- Scheduling
- Setup Time

7.  Simple Batch Systems
- Early computers were extremely expensive.
It is Important to maximize processor
utilization
- Monitor Point of View – Monitor controls the
sequence of events
- Processor Point of View – Processor executes
instruction from the memory containing the
monitor

8. - Job Control Language (JCL) – Special type of
programming language used to provide
instructions to the monitor
- Desirable Hardware Features
Memory protection for monitor
Timer
Privileged instructions
Interrupts
- Modes of Operation
- User Mode - user program executes in user
mode
- Kernel Mode - monitor executes in kernel
mode

9. Multiprogrammed Batch Systems
- Even with the automatic job sequencing provided
by a simple batch operating system, the processor
is often idle
- The problem is that I/O devices are slow
compared to the processor.
 Uniprogramming
- Processor must wait for I/O instruction to
complete before preceding

10.  Multiprogramming
- When one job needs to wait for I/O, the processor
can switch to the other job

11.  Time Sharing Systems
- Using multiprogramming to handle multiple
interactive jobs
- Processor’s time is shared among multiple users
- Multiple users simultaneously access the system
through terminals
Problems and Issues:
- Multiple jobs in memory must be protected from
each other’s data
- File system must be protected so that only
authorised users can access
- Contention for resources must be handled

12.  Major Theoretical advances in the development of
OS are:
- Processes
- Memory management
- Information protection and security
- Scheduling and resource management
- System structure

13.  Process is fundamental to the structure of
Operating Systems
 A definition of process in different terms is:
 A program in execution
 An instance of a running program
 The entity that can be assigned to and executed
on a processor
 A single sequential thread of execution, a current
state and an associated set of system resources

14.  Causes of Errors in the Design of the System
Software are:
 Improper synchronization
 Failed mutual exclusion
 Non-determinate program operation
 Deadlocks
 A process consists of three components
 An executable program
 Associated data needed by the program like
variables, buffer etc.,
 Execution context or process state of the
program

15.  The 5 principal storage management
responsibilities of OS are:
 Process isolation
 Automatic allocation and management
 Support of modular programming
 Protection and access control
 Long-term storage
- Virtual memory allows programs to address
memory from a logical point of view

16.  The growth in the use of time-sharing systems and
computer networks has brought with it a growth in
concern for the protection of information
 Four categories related with security and
protection in OS are:
 Availability
 Confidentiality
 Data integrity
 Authenticity

17.  Key responsibility of an OS is managing resources
like memory space, I/O devices and processors
 Resource allocation and scheduling policies must
consider the following parameters:
 Fairness
 Differential responsiveness
 Efficiency

18.  System structure consists of different levels
Level 1: Electronic circuits
Level 2: Instruction set
Level 3: Procedures
Level 4: Interrupts
Level 5: Primitive Processes
Level 6: Local secondary store
Level 7: Virtual memory
Level 8: Communications
Level 9: File system
Level 10: Devices
Level 11: Directories
Level 12: User processes
Level 13: Shell

19.  Wide range of different approaches and design
elements has been tried are fits into the following
categories
 Microkernel architecture
 Multithreading
 Symmetric multiprocessing
 Distributed operating systems
 Object-oriented design