Lecture 9

Operating System

• A special system software that acts as an intermediary between a user of a computer and the computer hardware.

• Provides an environment in which the user can execute programs/applications in a convenient and efficient manner.

Operating System

User

Operating System

Hardware

Examples of OS: Windows, MS-DOS, Linux, Unix

Operating System.

Thus the main goals for an Operating system are:

• Make computer convenient to use (hides Hardware details)• Utilize resources in efficient manner

Operating System

Computer hardware

Operating System

User

Application Software

Functions of O/S

1. Process Management2. Memory Management3. Deadlock Handling4. File Management5. I/O Management6. Protection & Security7. Job scheduling8. Interpretation of commands and instructions.9. Co-ordination of compilers and, assembler,

programs and other s/w of computer system.

Functions of O/S

10.Production of error messages.11.Maintenance of internal time clock and log

system usage for all users.12.Provides easy communication between the

computer system and users.13. Resource Allocator14. Intermediary15.Executes application software16.Memory management17.CPU Scheduling

CATEGORIES OF OPERATING SYSTEMS

Operating systems can be categorised by the number of users they support as well as by their level of sophistication.

Three categories are broadly recognized:-1. Desktop O/S:

• Designed to support a single user or a small work group of users.

2. Departmental O/S:• Supports from a few dozen to a few

hundred users.

CATEGORIES OF OPERATING SYSTEMS

3. Enterprise O/S: • Generally supports thousands of users

and transactions simultaneously. • Offers the greatest functionality, followed

by departmental operating systems, and then desktop operating systems.

• The user interface is the least sophisticated on enterprise operating systems.

Desktop Operating System


• Supports a single user or a small group of users.• Some examples of the operating systems in this

category are:-

1. MS-DOS: • One of the original operating systems for the

IBM PC and its clones. • A non-graphical, line oriented, command-

driven operating system, with a relatively simple interface but not a friendly user interface.

• It was not capable of multitasking.• It has now been almost totally replaced by

GUI products such as Windows 95, Windows 98, Windows 2000 and Windows XP.


2. Windows 3.1• It is a transition windowing system

between MS-DOS and Windows95, Windows 98 and Windows 2000.

• It is not actually an operating system, but a GUI that operates with, and extends the capabilities of MS-DOS


3. Windows 95• The first of a series of products in the

Windows operating systems that provides a GUI by using icons to provide instant access to common tasks.

• It is a 32-bit operating system that features multitasking, networking, and Internet integration capabilities.

• It also offers plug-and-play capabilities by enabling the operating system to recognize new hardware and install the necessary software (device drivers) automatically.


4. Windows 98• Offered minor refinements, bug fixes, and

enhancements to windows 95. 5. Windows NT• An operating system for high-end desktops

and workstations.• It provides the same GUI as Windows 95, 98,

and 2000.• Has more powerful multitasking, and memory

management capabilities.• It is popular in networked systems in business

organizations.


6. Windows 2000• Microsoft changed the name of the upgrade of

Windows NT 5.0 to Windows 2000.• This operating system has added security

features.• Runs on multiprocessor computers.• Offers added Internet and Intranet

functionality. 7. Windows CE (Compact Edition)• Is a 32-bit operating system designed for

hand-held PCs, and wireless communication devices.


8. IBM’s OS/2 Operating System• A 32-bit operating system that supports

multitasking, and supports networked applications.

9. Macintosh Operating System• For Apple Macintosh microcomputers.• Is a 32-bit operating system that features

multitasking and powerful graphics capabilities.


10.Unix

• Provides many sophisticated desktop features, including multiprocessing and multitasking techniques.

• Is valuable to business organizations because it can be used on many different sizes of computers ( different hardware: non Intel and Intel processors).

• Was popularized by Sun Microsystems.


11. Linux• A powerful version of Unix .• Completely free of charge.• It offers multitasking, virtual memory management,

and TCP/IP networking.• Originally written by Linus Tovalds at the University of

Helsinki in 1991. • He then released the source code to the world.• Like Unix, it runs on multiple hardware platforms.• Is becoming widely used by Internet service

providers.• The clearinghouse for Linux information on the

Internet may be found at www.linuxhq.com

12.Java Operating System

• Is designed for hand-held products and network computers.

• Sun’s java operating system executes programs written in Java language without the need for a traditional operating system.

• It is designed for Internet and Intranet applications and embedded devices.


Departmental Server OperatingSystems

The major departmental server operating systems include:-

• Unix• Windows NT server• IBM’s OS/2 Warp Server• Novell NetWare• IBM’s OS/400



Although some of these are also desktop OS, all can serve as departmental server OS because of their:-

• Strong scalability• Reliability• Backup• Security26• Fault tolerance• Multitasking• Multiprocessing• TCP/IP networking• Network management

Enterprise Operating Systems


The major enterprise operating systems include:

• IBM’s MVS (Multiple Virtual Storage)• IBM’s VM (Virtual Machine)• IBM’s VSE (Virtual Storage Extended)• Digital Open VMS (Virtual Machine System)


Enterprise operating systems support: • Secure electronic commerce• Multiple concurrent users • Large (terabyte) databases• Millions of transactions per day.

Types of O/S

• Multitasking• Multiprogramming• Time sharing• Multiprocessing

MULTITASKING O/S

• Executing more than one task concurrently.• Execution of two or more tasks/programs by

one user concurrently on the same computer with one central processor.

• For example, the user may be running one program and simultaneously listening to a music file.

Multiprogramming Operating System

• Refers to concurrent execution of different users’ programs on a machine with a single processor.

• It is the execution of two or more programs concurrently on a multi-user operating system.

• The processor spends a certain amount of time executing each user’s program. As the processor works much faster, it seems as though all the programs are being run at the same time.

Time Sharing Operating System

• Round-Robin processing of programs for several users.

• A single computer processes the tasks of several users at different locations based on the concept of time slicing between the users.

Multiprocessing Operating System

• Simultaneous processing of two or more programs by multiple computers or processors linked together to perform work simultaneously.

• This can involve processing of instructions from different programs or different instructions within the same program simultaneously.

• Implemented using concepts of parallel processing.

Real Time Operating System• an operating system that guarantees a certain

capability within a specified time constraint• Such applications include embedded systems and

scientific research equipment.• Provides facilities which, if used properly, guarantee

deadlines can be met. • Uses specialized scheduling algorithms in order to

provide the real-time developer with the tools necessary to produce deterministic behavior in the final system.

• An RTOS is valued more for how quickly and/or predictably it can respond to a particular event

• An early example of a large-scale real-time operating system was the so-called "control program" developed by American Airlines and IBM for the Sabre Airline Reservations System.

Technology

Lecture 9