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The Evolution of Operating Systems :. The single processing machines of 1940’s and 1950’s were not very flexible or efficient. The processing is divided into 3 parts: Batch Processing : The execution of jobs by collecting them in a batch

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the evolution of operating systems
The Evolution of Operating Systems :
  • The single processing machines of 1940’s and 1950’s were not very flexible or efficient.
  • The processing is divided into 3 parts:
  • Batch Processing:The execution of jobs by collecting them in a batch

- The jobs resides in mass storage waited for execution in a job queue

- The job queue is referred to term First-In-First-Out (FIFO)

-In early batch processing systems, each job was accompanied by a set of instruction explaining the steps require preparing the machine for that particular job.These instructions are called the Job Control Language(JCL)

the evolution of operating systems1

Jobs,Program, Data, and Directions

Results

User Domain

FIFO

Job Queue

Job Execution

Machine Domain

The Evolution of Operating Systems :
  • Batch Processing:
the evolution of operating systems2

Program, Data, Directions, and Results

User Domain

Machine Domain

Program Execution

The Evolution of Operating Systems :
  • Interactive Processing:These systems allow the execution of programs that carried on a dialogue with the userthrough remote terminals or workstations

- These interactive systems gave birth of the concept known as real-time processing , which refers to the requirement that the activities taking place in a machine must be coordinated with the activities in the machine’s environment

the evolution of operating systems3

Time Slice

P1

P2

P3

P1

The Evolution of Operating Systems :
  • Time-Sharing : technique of dividing time into intervals , or time slices, and then restricting the execution of a job(process) to only one time slice .

- At the end of each time slice, the current job is set aside and another is allowed to execute during the next time slice

- By rapidly shuffling of the jobs in this manner, the illusion of several jobs executing simultaneously is created

-Today, time-sharing is used

in single-user systems as well as

multi user systems, the former

is called multitasking

multiprocessor systems
Multiprocessor Systems :
  • The word multiprocessor refers to just one computer contains several processors
  • Coupled computer systems is called a network
  • The concept of network refers to many small computers connected via network in which users share resources(such as printing capabilities, software packages, data storage facilities, and information) scattered throughout the system
  • The Internet is an example of a network
operating system architecture

Software

Application

System

Utility

Operating System

Shell

Kernel

Operating System Architecture :
  • To understand the architecture of a typical operating system(O S), it is helpful to grasp the complete spectrum of software found within a typical computer system
  • We group pieces of software according to the following classification scheme:
o s architecture
O.S Architecture :
  • Application Software (AS):Consists of the programs for performing tasks particular to the machine’s utilization

- Examples of application software include spreadsheets, database systems, publishing systems, program development software , and games

  • System Software : performs those tasks that are common to computer systems in general.

- Provides the environment in which the A.S resides.

- Within the class of system software there two categories:

  • Operating System (OS)
  • Utility Software (US):

- Consists of Software units that extend the capabilities of OS

- The distinction between AS and US and between US and OS is often vague

o s architecture1

User

User

O.S

User

O.S Architecture :
  • Consists of two parts:
  • The Shell
  • The Kernel

The Shell :

- The part of the OS that defines the interface between the operating system and its users

- The job of the shell is to communicate with the user, or users , of the machine. Modern shells perform this task by means of Graphical User Interface (GUI)

the kernel
The Kernel :
  • The internal part of OS, contains those software components that perform the very basic functions required by the computer installation
  • The kernel consists of the following components:
  • File Manager
  • Device Drivers
  • Memory Manager
  • Scheduler
  • Dispatcher
boot strapping booting

Main Memory

Disk Storage

Bootstrap Program

Bootstrap Program

ROM

Operating System

Operating System

Volatile

Memory

Operating System

Boot strapping (Booting) :
  • The procedure performed by the machine each time it turned on
  • The booting in special-purpose machines performed through the ROM which contains the main part of OS
  • In general-purpose machines, the ROM contains a short program called the bootstrap , this program executed automatically when the machine is turned on which directs the CPU through the process of transferring material from a predetermined location in mass storage into the volatile area of main memory
coordinating the machine s activities
Coordinating the Machine’s Activities :

The Concept of a Process :

  • The program is merely a static set of directions, while the process is a dynamic activity whose properties change as time progresses
  • A process encompasses the current status of the activity called the process state, this state includes:
  • The current position in the program being executed(the value of the program counter)
  • The value of other CPU registers
  • The associated memory cells
  • At different times during the execution of a program( at different times in a process) different snapshots(different process states) will be observed
process administration
Process Administration :
  • The tasks associated with process coordination are handled by the scheduler and dispatcher within the operating system’s kernel

The Scheduler :

  • To keep track of all the processes, the scheduler maintains a block of information in main memory called the process table
  • Each time a new task is assigned to the machine, the scheduler creates a process for that task by placing a new entry in the process table
  • The entry contains such information as

- The memory area assigned to the process(obtained from the memory manager) , the priority of the process, andwhether the process is ready or waiting

  • The Scheduler maintains this information as the process progresses. The process will shift back and forth between ready and waiting
  • The priority of the process changes as time passes
  • The scheduler must remove the process from the process table when the process is completed
the dispatcher

Interrupt

Interrupt

Interrupt

Interrupt

Process B

Process B

Process Switch

Process Switch

Process Switch

Process A

Process A

Advancing Time

The Dispatcher :
  • Ensures that the scheduled processes are actually executed
  • In time-sharing system this task is accomplished by dividing time into short segments, each called a time slice or quantum(typically about 50 ms)
  • Switching the CPU’s attention among the processes as each allowed to execute for no longer than one time slice process switch
  • Dispatcher initiates a timer circuit that will measure the next quantum
  • At the end of the quantum the timer circuit generates a signal called an interrupt
the client server model

Requests

Client

Server

Service

S C

C

S

C

C

C

S

C

S

The Client/Server Model :
  • The various units within an operating system normally execute as individual processes
  • To coordinate their activities, these processes must communicate with one another
  • To simplify this interprocess communication, the components of OS are often designed to conform to the client/server model
handling competition among processes
Handling Competition Among Processes :
  • A universal task among the components of OS’s kernel is the allocation of the machine’s resources to the processes in the system.
  • This allocation task may has several problems that can lead to system malfunctions unless they accounted for.
  • Semaphores
  • Deadlock
semaphores
Semaphores :
  • Consider the printer example where two users send a file to the printer
  • Access allocation requires that the OS keeps track whether the printer has been allocated. One approach is to use flag(Set + Clear)
  • Clear: means the printer is available
  • Set: means that the printer is busy
  • The OS clears the flag to begin, then it checks the flag each time a request for printer access is made. If the flag is set the OS makes the request wait.

Two solutions Test-and-Set and Interrupt Enable and Disable

deadlock
Deadlock :
  • Two processes are blocked from processing because each is waiting for access to resources allocated to another. Like a printer waiting for tape drive while the tape drive is waiting for the printer
  • Analysis of deadlock has revealed that it cannot occur unless all three of the following conditions are satisfied:
  • There is a competition for non-sharable resources
  • The resources are requested on a partial basis; that is, having received some resources, a process will return later to request more
  • Once a resource has been allocated, it can not be forcibly retrieved
networks
Networks :
  • Networks are classified as :
  • Local Area Networks(LANs) and Wide Area Networks (WANs) :

LAN: Normally consists of collection of computers in a single building or building complex

WAN: Links machines that may be on opposite sides of a city or the world, like satellite link

  • Closed Networks and Open Networks:

Closed Network:Network comprised of HW and SW from a single vendor

Open Network: Implemented as a conglomerate of products from different manufactures (e.g. Internet)

  • Topology of the network
networks1
Networks
  • Topology of the network: the pattern in which the machines are connected:

- Ring topology

- Bus topology

- Star topology

- Irregular topology

  • Internet
  • Internet addressing
  • WWW
network protocols

Computer

Computer

Computer

Messages move in only one direction

Computer

Computer

“Communication over ring topology”

Network Protocols :
  • Controlling Transmission Privileges :
the layered approach to network software

Message’s Origin

Message’s Destination

Application Layer

Application Layer

Transport Layer

Transport Layer

Network Layer

Network Layer

Link Layer

Link Layer

Internet Software Layers

The Layered Approach to Network Software :
the layered approach to network software1

Application

Transport

Application

Network

Transport

Network

Link

Network

Network

Link

Link

Link

The layered Approach to Network Software :

A Path of a data unit through the Internet involving two intermediate machines