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Operating system lect3 Autosaved.pptx
- 2. Objectives To get familiar with popular OS like Unix, Linux and Windows. Understand the structure of OS. Types of OS Evolution of OS
- 3. OS Structure The approach of interconnecting and integrating multiple operating system components into the kernel can be described as an operating system structure. Simple Structure Monolithic Structure Layered Approach Micro-kernel
- 4. Simple Structure It is the simplest Operating System Structure and is not well defined; It can only be used for small and limited systems. In this structure, programs can access I/O routines which can cause unauthorized access to I/O routines. If one user program fails, the entire operating system gets crashed. The abstraction level in MS-DOS systems is low, so programs and I/O routines are visible to the end-user, so the user can have unauthorized access.
- 6. Advantages and Disadvantages Advantages of Simple Structure It is easy to develop because of the limited number of interfaces and layers. Offers good performance due to lesser layers between hardware and applications. Disadvantages of Simple Structure If one user program fails, the entire operating system crashes. Abstraction or data hiding is not present as layers are connected and communicate with each other. Layers can access the processes going in the Operating System, which can lead to data modification and can cause Operating System to crash.
- 7. Monolithic Structure The Monolithic operating System in which the kernel acts as a manager by managing all things like file management, memory management, device management, and operational processes of the Operating System. The kernel is the heart of a computer operating system (OS). Kernel delivers basic services to all other elements of the System. It serves as the primary interface between the Operating System and the hardware.
- 8. Monolithic Structure The monolithic kernel functions as a virtual machine by working on top of the Operating System and controlling all hardware components. This is an outdated operating system that was used in banks to accomplish minor activities such as batch processing and time-sharing, which enables many people at various terminals to access the Operating System.
- 10. Advantages and Disadvantages Advantages of Monolithic structure: It is simple to design and implement because all operations are managed by kernel only, and layering is not needed. As services such as memory management, file management, process scheduling, etc., are implemented in the same address space, the execution of the monolithic kernel is relatively fast as compared to normal systems. Using the same address saves time for address allocation for new processes and makes it faster. Disadvantages of Monolithic structure: If any service in the monolithic kernel fails, the entire System fails because, in address space, the services are connected to each other and affect each other. It is not flexible, and to introduce a new service
- 11. Layered Approach Layered Structure is a type of system structure in which the different services of the operating system are split into various layers, where each layer has a specific well-defined task to perform. It was created to improve the pre-existing structures like the Monolithic structure ( UNIX ) and the Simple structure In this approach, functionalities of each layer are isolated, and abstraction is also available. The Windows NT operating system uses this layered approach as a part of it.
- 13. Layered Structure of Computer program Users Humans Application software- web browsers/gaming System software- compiler/interpreter/shell(programming layer that understands the problems) Operating system hardware
- 14. Services at user levels Execution of our programs Download required programs Handling errors Access to Input/Output devices Controlled access to files
- 15. Services at system levels Handling new services Handling updates Dealing with resource allocation based issues. Controls users functions Monitors data
- 16. Services at hardware levels Allocation of resources Controlled execution of the program Computer operations of i/o devices Protection of resources Data monitoring
- 17. Advantages and Disadvantages Advantages of Layered Structure Each layer has its functionalities, so work tasks are isolated, and abstraction is present up to some level. This design promotes modularity as each layer performs only the tasks it is scheduled to perform. A modification made in a particular layer will not affect the other layers. Disadvantages of Layered Structure In Layered Structure, layering causes degradation in performance. It takes careful planning to construct the layers since higher layers only utilize the functions of lower layers.
- 18. Micro-kernel Micro-Kernel structure designs the Operating System by removing all non- essential components of the kernel. These non-essential components of kernels are implemented as systems and user programs. Hence these implemented systems are called as Micro-Kernels. Each Micro-Kernel is made independently and is isolated from other Micro- Kernels. So this makes the system more secure and reliable. If any Micro- Kernel fails, then the remaining operating System remains untouched and works fine.
- 19. Micro-kernel
- 20. Advantages and Disadvantages Advantages of Micro-kernel structure: As each Micro-Kernel is isolated, it is safe and trustworthy. Because Micro-Kernels are smaller, they can be successfully tested. If any component or Micro-Kernel fails, the remaining operating System is unaffected and continues to function normally. Disadvantages of Micro-kernel structure: Increased inter-module communication reduces system performance. System is complex to be constructed.
- 21. UNIX OS UNIX is a powerful Operating System initially developed by Ken Thompson, Dennis Ritchie at AT&T Bell laboratories in 1970. It is prevalent among scientific, engineering, and academic institutions due to its most appreciative features like multitasking, flexibility, and many more. In UNIX, the file system is a hierarchical structure of files and directories where users can store and retrieve information using the files.
- 23. Features of UNIX OS Multitasking: A UNIX operating system is a multitasking operating system that allows you to initiate more than one task from the same terminal so that one task is performed as a foreground and the other task as a background process. Multi-user: UNIX operating system supports more than one user to access computer resources like main memory, hard disk, tape drives, etc. Multiple users can log on to the system from different terminals and run different jobs that share the resources of a command terminal. It deals with the principle of time-sharing. Time-sharing is done by a scheduler that divides the CPU time into several segments also called a time slice, and each segment is assigned to each user on a scheduled basis. This time slice is tiny. When this time is expired, it passes control to the following user on the system. Each user executes their set of instructions within their time slice.
- 24. Features of UNIX OS Portability: This feature makes the UNIX work on different machines and platforms with the easy transfer of code to any computer system. Since a significant portion of UNIX is written in C language, and only a tiny portion is coded in assembly language for specific hardware. File Security and Protection: Being a multi-user system, UNIX makes special consideration for file and system security. UNIX has different levels of security using assigning username and password to individual users ensuring the authentication, at the level providing file access permission viz. read, write and execute and lastly file encryption to change the file into an unreadable format. Command Structure: UNIX commands are easy to understand and simple to use. Example: "cp", mv etc. While working in the UNIX environment, the UNIX commands are case-sensitive and are entered in lower case. Communication: In UNIX, communication is an excellent feature that enables the user to communicate worldwide. It supports various communication facilities provided using the write command, mail command, talk command, etc.
- 25. Features of UNIX OS Open Source: UNIX operating system is open source it means it is freely available to all and is a community-based development project. Accounting: UNIX keeps an account of jobs created by the user. This feature enhances the system performance in terms of CPU monitoring and disk space checking. It allows you to keep an account of disk space used by each user, and the disk space can be limited by each other. You can assign every user a different disk quota. The root user can perform these accounting tasks using various commands such as df(availability of disk space), du(disk usage), etc. UNIX Tools and Utilities: UNIX system provides various types of tools and utilities facilities such sed(search editors, used for editing scripts) and awk, etc. Some of the general-purpose tools are compilers, interpreters, network applications, etc. It also includes various server programs which provide remote and administration services.
- 26. Structure of Unix OS
- 27. Shell The Shell is an interpreter that interprets the command submitted by the user at the terminal, and calls the program you simply want. It also keeps a history of the list of the commands you have typed in. If you need to repeat a command you typed it, use the cursor keys to scroll up and down the list or type history for a list of previous commands.
- 29. Types of Shell in UNIX Bourne Shell: This Shell is simply called the Shell. It was the first Shell for UNIX OS. It is still the most widely available Shell on a UNIX system. C Shell: The C shell is another popular shell commonly available on a UNIX system. The C shell was developed by the University of California at Berkeley and removed some of the shortcomings of the Bourne shell. Korn Shell: This Shell was created by David Korn to address the Bourne Shell's user-interaction issues and to deal with the shortcomings of the C shell's scripting quirks. It has more programming features.
- 30. Linux OS The Linux OS was developed by Linus Torvalds in 1991, which sprouted as an idea to improve the UNIX OS. He suggested improvements but was rejected by UNIX designers. Therefore, he thought of launching an OS, designed in a way that could be modified by its users. Nowadays, Linux is the fastest-growing OS. It is used from phones to supercomputers by almost all major hardware devices.
- 32. Structure of Linux OS Kernel: Linux kernel is the core part of the operating system. It establishes communication between devices and software. Moreover, it manages system resources. 2) System Libraries System libraries are special programs that help in accessing the kernel's features. A kernel has to be triggered to perform a task, and this triggering is done by the applications. But applications must know how to place a system call because each kernel has a different set of system calls. Programmers have developed a standard library of procedures to communicate with the kernel. Each operating system supports these standards, and then these are transferred to system calls for that operating system. The most well-known system library for Linux is Glibc (GNU C library).
- 33. Structure of Linux OS The most well-known system library for Linux is Glibc (GNU C library). 3) System Tools Linux OS has a set of utility tools, which are usually simple commands. It is a software which GNU project has written and publish under their open source license so that software is freely available to everyone. With the help of commands, you can access your files, edit and manipulate data in your directories or files, change the location of files, or anything.
- 34. Structure of OS 4) Development Tools With the above three components, your OS is running and working. But to update your system, you have additional tools and libraries. These additional tools and libraries are written by the programmers and are called toolchain. A toolchain is a vital development tool used by the developers to produce a working application. 5) End User Tools These end tools make a system unique for a user. End tools are not required for the operating system but are necessary for a user. Some examples of end tools are graphic design tools, office suites, browsers, multimedia players, etc.
- 36. Any Query???
Editor's Notes
- #30: Application programs For Example:油emacs editor, StarOffice, xv image viewer, g++ compiler etc.