Kernel. What is an Operating System? Systems Software and Application Software. The core of an OS is called kernel, which. Module 9: Operating Systems

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CP102 Module 9: Operating Systems 1

Module 9: Operating Systems

Objective

• What is an operating system (OS)? OS kernel, and basic functions • OS Examples: MS-DOS, MS Windows, Mac OS Unix/Linux • Features of modern OS

– Graphical operating system – Multiple users, secure, stable – Support networks

• The main issues that an OS deals with

– Resource allocation, CPU time, memory management – Multiprocessing, time-sharing, multiprogramming

• Utility programs

Systems Software and Application Software

• Software are classified into categories according to their functions: system software, application software

– System software are programs related to coordinating computer operations, E.g.

• Operating systems • Language translators

– Convert program code to machine-readable form

– Utility programs are those application

programs performing secondary chores

What is an Operating System ?

• A set of programs that lies between applications software and the hardware

– Manages computer’s resources (CPU, memory, peripheral devices)

– Establishes a user interface • Determines how user

interacts with operating system

– Provides and executes services for application software

Kernel

• The core of an OS is called kernel, which

– Is loaded from hard drive into memory when

computer is booted and stays as long as the

computer is running

• Booting refers to starting the computer

– Manages the operating system

• Loads other operating system programs from disk storage as needed

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Examples of Operating Systems

• Platform:

combination of computer hardware

and operating system software

• Common Platforms

– PC with MS DOS (disk operating system), Windows – MAC OS

– PC and Unix/Linux

MS-DOS

• Uses a command-line interface

– Screen provides prompts for user. User types commands. – Five basic commands: dir, mkdir, cd, copy, del.

• Largely replaced by graphical user interfaces • Not user-friendly

• It is still there ( demo )

Microsoft Windows

• Began as an operating environment for MS-DOS – Not a full-blown operating system; required

MS-DOS

• Uses a graphical user interface

– Users can use DOS commands and interface • Now a complete family of operating systems

Brief history of Windows OS

– Microsoft Windows 1.0, 1985 – Microsoft Windows 2.0, 1987 – Microsoft Windows 3.0, 1990 – Windows 3.1, 1992

– Windows 95, 1995

sells more than 1 Million copies within 4 days.

– Windows 98

– Microsoft Windows 2000 – Microsoft Windows XP, 2001 – Other MS Windows OS product lines

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Graphical User Interface

• User clicks an icon to perform tasks

• Start Menu in lower left corner launches programs • Use menus to activate

commands

• Other features

– Long file names (up to 255 characters)

– Plug and Play

• Makes installing hardware components easier

Windows NT

• Windows 98 and early is for single user

• Windows NT was designed for corporate

networked environments

– Be able to handle many users

– Engineered for scalability

– Stronger security

Windows 2000

• The generation of Windows NT

• One computer “serves” many users

– You identify yourself and the system knows

your preferences

– You get “your” desktop and files, regardless of

which PC you use to log into the network

Windows XP

• Brings consumer and corporate versions of

Windows together into a single product

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Windows XP Enhancements

• Improved user interface

– Much clearer and uncluttered desktop – More icons on redesigned Start Menu

• Improved multimedia support

• More personalization

• Multiple user support

– User can log off, leaving programs running, and allow another user to log on

– Set up limited accounts for children to use; i.e., no inappropriate games or no Internet access

• Internet support and protection

Windows CE

• Scaled-back version of Windows 9x

– Designed to work on machines with small

screens and little, if any, storage

– Used in Pocket PCs

– Used in mobile phone

– Used in embedded systems

• Computer devices integrated into other products; i.e., robots

MAC OS

• Designed for the Macintosh computer

• First commercially successful GUI

– Has served as the model for Windows and other GUI products developed since then

UNIX

• Developed in 1971 for use on the DEC minicomputer • Not tied to any family of processors

– Runs on just about every type of system

• Run on most main frame, supercomputers, Sun workstations, PC

• Primary operating system in use on Internet servers

– E.g. main web server of WLU is running Unix

• Features

– Very reliable, secure, stable system.

– Character-based system with command-line interface, now comes with several graphic user interface

– Handles many simultaneous users easily – Multiple tasks

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Linux

• Similar to Unix, but in open source domain

• Uses command-line interface

– Many companies have created a GUI to work with Linux

• Open-source concept

– Source code is free

– Users can download, change, and distribute the software

• More stable than Windows

• Applications relatively scarce

Simple Unix/Linux Commands

ls, ls –l, ls -a mkdir cd, cd .. pwd mv cp rm rmdir cat, less, tail grep who chmod

Operating Systems for Networks

• Network operating system (NOS)

– Handles network functions

– Make resources appear as though they were

running from client computers

– Common systems

• Functions

– Sharing resources (hard disks and printers)

– Data security

– Administrative control

Examples of Network Operating Systems

• Windows NT Server

• Windows 2000 Server

• Novell Netware

• Unix

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The Main Task of an Operating Systems

• Resource allocation: assigning and computer resources to certain programs and processes for their use • This problem was raised when people designed the OS

for large computers with multiple users. It is also a fundamental problem for modern OS for PC. • Main issues related to resource allocation

– Sharing the Central Processing Unit – Sharing memory

– Sharing storage resources – Sharing printing resources

Sharing the CPU

• Multiprogramming

– Two or more programs executed concurrently • Programs take turns using the CPU • Event-driven

– An interrupt suspends processing to allow another program to run

– After the second program runs, the operating system returns the CPU to another program

• Time-Sharing

– Programs take turns using the CPU – Time-driven

• Each user is given a slice of time (fraction of a second) • CPU works only on that user’s tasks during its time slice • Response time: the time between typed request and

computer’s reply

– Typically used in applications with many users

Multiprocessing

• The use of a powerful computer with multiple CPUs – Supper computers usually have many processors – Personal computers will soon have multiple

processors

• Multiple programs run simultaneously – Each runs on its own processor

Sharing Memory

• Memory management

– Divides memory into separate partitions – Allocates memory to programs

– Keeps programs separate from one another

• Sharing memory

– Divides memory into foreground and background – Uses virtual storage

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Foreground and Background

• Foreground: for programs with high priority that

will receive more CPU time

• Background: for programs with lower priority that

will receive less CPU time

– Programs waiting to run are kept in queues

based on their priority

Virtual Storage

• Programs currently executed are stored on disk

– Portions of program brought into memory as needed – Minimizes the amount of memory needed

• Can be implemented by paging

– Divide memory into small, fixed-size pages – Page table keeps track of memory locations