intro to OS

1. Welcome to Welcome to Operating System I Operating System I

2. Chapter Outline Chapter Outline Overview of Operating Systems ● What is an OS ● Brief history. ● 2 2

3. Overview of Operating Overview of Operating Systems Systems An Operating System (OS) is an interface between a computer user and computer hardware. An operating system is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers. Following are some of important functions of an operating System. Memory Management Processor Management Device Management File Management Security Control over system performance Job accounting Error detecting aids Coordination between other software and users 3 3

4. What is an OS What is an OS 4 4

5. What is an OS What is an OS 5 5

6. History of OS History of OS Operating systems were first developed in the late 1950s to manage tape storage The General Motors Research Lab implemented the first OS in the early 1950s for their IBM 701 In the mid-1960s, operating systems started to use disks In the late 1960s, the first version of the Unix OS was developed The first OS built by Microsoft was DOS. It was built in 1981 by purchasing the 86-DOS software from a Seattle company The present-day popular OS Windows first came to existence in 1985 when a GUI was created and paired with MS-DOS.

7. Examples of Operating System with Market Share 7 7

9. Chapter 2 Background and Chapter 2 Background and Basics of an OS Basics of an OS

10. Chapter Outline Chapter Outline Computer System review ● Architecture Instruction cycle Process Control Block Basic OSs ● Batch Operating system Multi-programmed Operating system Time-sharing Computer System Structures ● Operating System Structures ● 10 10

11. Computer System Review Computer System Review A computer system is a basic, complete and functional hardware and software setup with everything needed to implement computing performance. 11 11

12. Computer System Review Computer System Review To look at the history of a computing system, you have to go all the way back to Charles Babbage's differential machine. This computer, (which never actually got fully built), predated and prefigured the mainframes and large-scale computers of the early 20th century the Von Neumann machine and its ilk, as computers, bulky and monolithic, first appeared in the human world. 12 12

13. Computer System Review Computer System Review The Personal Computer Then, the personal computer or desktop computer was born. This model persisted for a long time, where the computer box or shell was the central hardware and used peripherals like a monitor, keyboard and mouse, along with software that was fed to the computer through floppy disks. Operating System The operating system emerged early as a convention in supporting the full computing system in the box, and making sure that users had a universal way to handle the software that ran on that hardware. Laptops Over time, as Moore's law continued to apply and hardware became smaller, the laptop computer was born. Then came the mobile phone, and eventually the peripheral interface model with the plugged-in mouse, keyboard and monitor was replaced by a single touch screen device, so that no peripherals were needed. Then, in addition to the operating system, we learned about files, applications, and executables, the actual software products delivered to run on a given operating system. 13 13

14. Computer System Review Computer System Review The Cloud At the same time, a key software advance applied, too. Cloud and software as a storage models meant that software came to be delivered digitally through the Internet, instead of being sold on physical media like floppy disks and later, compact discs. “Out of the box” software became somewhat obsolete, especially in enterprise IT. Virtualization More recently, virtualization revolutionized how we think of hardware and software setups. A modern computing system may not consist of a piece of hardware itself — it may instead consist of a virtualized computer system or virtual machine that uses resources from a grid to operate. So what we think of as a computing system has changed in form, but not, in key ways, in substance. It still has all of those core capabilities: receiving user input, processing data, and storing information — it just does them in much more elegant and capable ways. As the interface evolves, and as we approach a new world of AI and machine learning, we see what power computing systems can have 14 14

15. Computer System Architecture Computer System Architecture Computer architecture is the organization of the components making up a computer system and the semantics or meaning of the operations that guide its function. As such, the computer architecture governs the design of a family of computers and defines the logical interface that is targeted by programming languages and their compilers. The organization determines the mix of functional units of which the system is composed and the structure of their interconnectivity. 15 15

16. Components in the Computer Components in the Computer System Architecture System Architecture 16 16

17. Computer System Instruction Computer System Instruction Cycle Cycle The instruction cycle is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of four main stages: the fetch stage, the decode stage, Read the effective address from memory. and the execute stage. 17 17

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19. Process Control Block Process Control Block Process control block (PCB) is a data structure which is associated with any process and provides all the complete information about that process. The process control block is "the manifestation of a process in an operating system". Process control block is important in multiprogramming environment as it captures the information pertaining to the number of processes running simultaneously.

20. Role of process control block Role of process control block The role or work of process control block (PCB) in process management is that it can access or be modified by most OS utilities including those that are involved with memory, scheduling, and input / output resource access. It can be said that the set of the process control blocks give the information of the current state of the operating system. 

21. Information Contained by the PCB Information Contained by the PCB ● Naming the process ●State of the process ●Resources allocated to the process ●Memory allocated to the process ●Scheduling information ●Input / output devices associated with process 21 21

22. Components of the PCB Components of the PCB Process ID: In computer system there are various process running simultaneously and each process has its unique ID. This Id helps system in scheduling the processes. This Id is provided by the process control block. In other words, it is an identification number that uniquely identifies the processes of computer system. Process state: As we know that the process state of any process can be New, running, waiting, executing, blocked, suspended, terminated. For more details regarding process states you can refer process management of an Operating System. Process control block is used to define the process state of any process. In other words, process control block refers the states of the processes. 22 22

23. Components of the PCB Components of the PCB Program counter: Program counter is used to point to the address of the next instruction to be executed in any process. This is also managed by the process control block. Register Information: This information is comprising with the various registers, such as index and stack that are associated with the process. This information is also managed by the process control block. 23 23

24. Basic Operating System Basic Operating System ●Types of OS Batch Operating system Multi-programmed Operating system Time-sharing Operating System Real Time Operating System 24 24

25. Batch Operating System Batch Operating System ●This type of operating system does not interact with the computer directly.(eg IBMs MVS OS) ●There is an operator which takes similar jobs having the same requirement and group them into batches. It is the responsibility of the operator to sort jobs with similar needs. 25 25

26. Advantages and disadvantages of Batch OS Advantages and disadvantages of Batch OS Advantages Disadvantages It is very difficult to guess or know the time required for any job to complete. Processors of the batch systems know how long the job would be when it is in queue The computer operators should be well known with batch systems • • Batch systems are hard to debug • It is sometimes costly • Multiple users can share the batch systems • The other jobs will have to wait for an unknown time if any job fails • The idle time for the batch system is very less • It is easy to manage large work repeatedly in batch systems • 26 26

27. Multi-programmed Operating system Multi-programmed Operating system ●Multiprogramming operating system has ability to execute multiple programs with using of only one processor machine(eg UNIX ). ●Main objective of multiprogramming is to manage entire resources of the system. The primary components of multiprogramming system are command processor, file system, I/O control system, and transient area. ●In the multiprogramming system, multiple users can perform their tasks concurrently, and it can be stored into main memory 27 27

28. Multi-programmed Operating system Multi-programmed Operating system 28 28

29. Advantages and disadvantages of multiprogramming OS Advantages and disadvantages of multiprogramming OS Disadvantages Advantages CPU scheduling is needed. To increase CPU utilization and it never gets idle. • • Memory management is required because all types of jobs are stored in the main memory. • Resources are utilized smartly. • Less response time • If, it contains massive load of jobs then its long time jobs have to need long waiting time. • Short time jobs are done fastest compare to long time jobs. • Multiple users can use multiprogramming system at once. Harder task is to manage of all processes and jobs. • • It can help to execute multiple tasks in single application at same time duration. It is highly complex and sophisticated. • • 29 29

30. Time Sharing Operating system Time Sharing Operating system ●Each task is given some time to execute so that all the tasks work smoothly (eg Multics,windows server 2000,windows NT server). ● Each user gets the time of CPU as they use a single system. These systems are also known as Multitasking Systems. The task can be from a single user or different users also. ●The time that each task gets to execute is called quantum. After this time interval is over OS switches over to the next task. 30 30

31. Time Sharing Operating system Time Sharing Operating system 31 31

32. Advantages and disadvantages of Time-Sharing OS Advantages and disadvantages of Time-Sharing OS Disadvantages Advantages Reliability problem Each task gets an equal opportunity • • One must have to take care of the security and integrity of user programs and data Fewer chances of duplication of software • • CPU idle time can be reduced • . Data communication problem • • 32 32

33. Real Time Operating system Real Time Operating system ● These types of OSs serve real-time systems. The time interval required to process and respond to inputs is very small. This time interval is called response time. (VRTX, Lynx, RT Linux) ● Real-time systems are used when there are time requirements that are very strict like missile systems, air traffic control systems, robots, etc. ● Two types of Real-Time Operating System which are as follows: Hard Real-Time Systems( RT linux): These OSs are meant for applications where time constraints are very strict and even the shortest possible delay is not acceptable. These systems are built for saving life like automatic parachutes or airbags which are required to be readily available in case of any accident. Virtual memory is rarely found in these systems. Soft Real-Time Systems: These OSs are for applications where for time-constraint is less strict. 33 33

34. Advantages and disadvantages of Real Time OS Advantages and disadvantages of Real Time OS Disadvantages Advantages Limited Tasks: Very few tasks run at the same time and their concentration is very less on few applications to avoid errors. • Maximum Consumption: Maximum utilization of devices and system, thus more output from all the resources • Task Shifting: The time assigned for shifting tasks in these systems are very less. For example, in older systems, it takes about 10 microseconds in shifting one task to another, and in the latest systems, it takes 3 microseconds. Use heavy system resources: Sometimes the system resources are not so good and they are expensive as well. • • Complex Algorithms: The algorithms are very complex and difficult for the designer to write on. • Focus on Application: Focus on running applications and less importance to applications which are in the queue. • Device driver and interrupt signals: It needs specific device drivers and interrupts signals to respond earliest to interrupts.34 • Real-time operating system in the embedded system: Since the size of programs are small, RTOS can also be used in embedded systems like in transport and others. • 34

35. Examples of RTOS Examples of RTOS 35 35

36. Computer system structure Computer system structure SEE SLIDE 16 36 36

37. Operating system structure Operating system structure An operating system is a construct that allows the user application programs to interact with the system hardware. Since the operating system is such a complex structure, it should be created with utmost care so it can be used and modified easily. An easy way to do this is to create the operating system in parts. Each of these parts should be well defined with clear inputs, outputs and functions. 37 37

38. Operating system structure Operating system structure Simple Structure There are many operating systems that have a rather simple structure. These started as small systems and rapidly expanded much further than their scope. A common example of this is MS- DOS. It was designed simply for a niche amount for people. There was no indication that it would become so popular. 38 38

39. Operating system structure Operating system structure 39 39

40. Operating system structure Operating system structure Layered Structure One way to achieve modularity in the operating system is the layered approach. In this, the bottom layer is the hardware and the topmost layer is the user interface. An image demonstrating the layered approach is as follows −Layered Structure 40 40