Lecture 11Operating Systems

Network, Communication, OSI

Lecturer: Sumaira Hussain

S.M.I University

Operating System

An operating system (OS) is software that manages computer hardware and software resources and provides common services for computer programs

Core Tasks of an OSProcessor managementMemory managementDevice managementStorage managementApplication InterfaceUser Interface

Processor ManagementThe CPU executes each process a bit at a time. The CPU's clock times the execution of a process, and when a time limit is reached, then the clock signals the CPU that it is time to switch to another process.

The CPU executes just one process, and the processes that are ready and waiting for their turn at execution are kept in a queue (a waiting line, like at the post office) in primary storage.

Memory ManagementStraight forward for a single-user, single taskingEach app must have enough private memory in which to executeApp can neither run into the private memory space of another app, nor be run into by another appDifferent types of memory (e.g. main, cache) in the system must be used properly, so that each app can run most effectively

Storage ManagementThe OS manages storage through one of its sub-modules, the File ManagerA file system is a collection of directories, subdirectories, and files organized in a logical order.File manager maintains an index of the filenames & where they are located on the disk.File manager make it easy to find the required file in a logical and timely fashion.

Device ManagementApplications talk to devices through the OS and OS talks to and manages devicesthrough Device DriversExample: When we print to a laser printer, we do not need to know its details. All wedo is to tell the printer device driver about what needs to be printed and it takes care of the details

Application InterfaceApp developers do not need to know much about the hardware, while they are developing their appThe OS provides all apps with a straight-forward and consistent interface to the HWExample: An app uses the OS to store data on the disk drive. For that, the app does not need to know about the exact physical characteristics of that drive; it just tells the OS to do that through the app interface, and the OS takes cares of all the details of the task

User InterfaceUsers communicate with the computer using a consistent user interface provided by the OSThis UI can be a command-line interface in which a user types in the commands.Example:

copy a:/file1.html c:/file1.htmlOr, it can be a graphical UI, where Windows, Icons, Menus, and a Pointing device (such as a mouse) is used to receive and display information. Example:With the help of the mouse, drag file1.html from drive a to drive c

Types of OS

Real-Time Operating System (RTOS)Single-User, Single TaskSingle-User, Multi-TaskingMulti-User

Real Time Operating SystemsUsed to run computers embedded in machinery, robots, scientific instruments and industrial systemsTypically, it has little user interaction capability, and no end-user utilities, since the system will be a "sealed box" when delivered for useExamples: Wind River, QNX, Real-time Linux, Real-time Windows NTAn important part of an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time every time it occursIn a complex machine, having a part move more quickly just because system resources are available may be just as catastrophic as having it not move at all because the systemwas busy

Single-User, Single TaskOS are designed to manage the computer so that one user can effectively do one thing at a timeThe Palm OS used in many palmtop computers (PDA’s) is an example of a single-user, single-task OS

Single-User, Multi-TaskingMost popular OSUsed by most all PC’s and LaptopsExamples: Windows, Mac OS, LinuxLets a single user interact with several programs, simultaneously

Multi-UserA multi-user OS allows many users to take advantage of the computer's resources, simultaneouslyThe OS must make sure that the requirements of the various users are balanced, and that the programs they are using each have sufficient and separate resources so that a problem with one user doesn't affect any of the other usersExamples: Linux, Unix, VMS and mainframe OS, such as MVS

Computer Communications Process in which two or more computers or devices transfer data, instructions, and information

Uses of Computing Communication

Internet E-Mail Instant Messaging FTP Newsgroups Chat Rooms Web Folders Fax Machine or Computer Fax/Modem Video Conferencing Internet telephony (enables you to talk to other people over the

Internet Sometimes called Voice over IP ) Internet printing (allows you to print to network printer from

anywhere in the world )

Computer NetworkMultiple computers that are connected together to share information and other resources

Components of Computer Networks

1. Computers2. Network Interface Cards (NIC)3. Hub4. Cables5. Routers6. Protocol

Network Interface Card

I/O device that plugs into the computerEnables it to communicate over a network

Hub

The network traffic controllerDevice that provides central point for cables in network Components of Conventional Computer Networks

CablesAre either electrical or opticalNot required at all for wireless networksWire, cable, and other tangible materials used to send communications signals

RoutersConnects computers and transmits data to correct destination on network Routers forward data on Internet using fastest available path

Protocol

Rules governing communications over the networkExample:OSI Model

OSI Model1)Application Layer

2)Presentation Layer

3)Session Layer

4)Transport Layer

5)Network Layer

6)Data Link Layer

7)Physical Layer

Type of Computer Networksaccording to the distance between nodes

LAN

MAN

WAN

LANNetwork in limited geographical area such as home or office building

MANconnects LANs in city or town

WANNetwork that covers large geographic area using many types of media

Internet is world’s largest WAN

Network Topologies

Client-ServerPoint to PointStarBusRing

Client-ServerOne or more computers act as server and other computers, or clients, access server

Point to PointSimple network that connects fewer than 10 computers

Each computer, or peer, has equal capabilities

BusAll computers and devices connect to central cable, or bus No server is requiredOne computer sends data to another by broadcasting the address of the receiver and the data over the busAll the computers in the network look at the address simultaneously, and the intended recipient accepts the data

RingCable forms closed ring, or loop, with all computers and devices arranged along ring

Data travels from device to device around entire ring, in one direction

No server is required

StarAll devices connect to a central device, called hub

All data transferred from one computer to another passes through hub

This topology allows multiple messages to be sent simultaneously