Operating Systems Lecture 1.pdf

Lecture 1 Fundamentals of Operating System By: Dr. Hajar Esmaeil As-Suhbani IT, 3rd Level  Outline  What is the Operating System?  Operating System Components  Storage Structure  User Interface  Differen...

Lecture 1 Fundamentals of Operating System By: Dr. Hajar Esmaeil As-Suhbani IT, 3rd Level  Outline  What is the Operating System?  Operating System Components  Storage Structure  User Interface  Different types of OS  OS services  System calls  System programs  OS structure 2  What is the Operating System?  Computer System = Hardware + Software  Software = Application Software + System Software(OS)  An operating system is: A program that manages the computer hardware.  It also provides a basis for application programs and acts as an intermediary/ interface between the user of the computer and the computer hardware.  Operating system goals:  Execute user programs and make solving user problems easier  Make the computer system convenient to use  Use the computer hardware in an efficient manner 3  Computer-System Components  Computer system can be divided into four components:  Hardware – provides basic computing resources  CPU, memory, I/O devices  Operating system – Controls and coordinates use of hardware among various applications and users  Application programs – define the ways in which the system resources are used to solve the computing problems of the users  Word processors, compilers, web browsers, database systems, video games Figure 1.1 Abstract view of the components of a computer system.  Users  People, machines, other computers 4  Operating System Definition  To understand more fully the operating system from role, we explore operating systems from two viewpoints:  User view: OS is an interface  Makes interfacing with the computer and running applications easy.  System view: OS is resource allocator  Controls and coordinates the hardware resources, services the application software (controls execution of programs to prevent errors ). 5  Some Important Terms  Kernel:  Kernel is a software code that reside in central core of OS.  It has complete control over system.  When operation system boots, kernel is first part of OS to load in main memory.  Kernel remains in main memory for entire duration of computer session.  Bootstrap program:  For a computer to start running it needs to have an initial program to run.  Bootstrap program is loaded at power-up or reboot  Typically stored in ROM or EPROM, generally known as firmware  Initializes all aspects of system  Loads operating system kernel and starts execution.  6  Storage Structure  Storage systems organized in hierarchy in terms of: Volatile  Speed  Cost Smaller size Loses its  Volatility contents when Expensive but fast power is removed Cost per bit decreases Larger Nonvolatile size Retains its contents even Access time increases when power is removed 7  …Storage Structure  Registers – used to store small piece of information (8, 32, 64 bits)  Cache – (access speed is very fast), used to store frequently used instructions e.g., For loop  Main memory – only large storage media that the CPU can access directly  Random access  Typically volatile  Various technologies becoming more popular  Secondary storage – extension of main memory that provides large nonvolatile storage capacity  Solid-state disks – faster than hard disks, nonvolatile  Hard disks – rigid metal or glass platters covered with magnetic recording material  Magnetic tapes – used on the olden days (obsolete) 8  User Interface  A user interface (UI) controls how you 2. Graphical user Interface enter data and instructions and how  With a graphical user interface (GUI), information is displayed on the screen you interact with menus and visual  There are three types of user interfaces: images. 1. Command Line Interface  In a command-line interface, a user types commands represented by short keywords or abbreviations or presses special keys on the keyboard to enter 3. Touch screen devices require new data and instructions. interfaces Here, users interact by making gestures on the touchscreen—for example, pressing and swiping fingers across the screen. 9  Types of OS  There are several types of Operating Systems in which many of which are mentioned below:  Batch Operating System  Multi-Programming System  Multi-Processing System  Multi-Tasking Operating System  Time-Sharing Operating System  Distributed Operating System  Network Operating System  Real-Time Operating System 10  Types of OS: Batch Operating System  This type of operating system does not interact with the computer directly.  There is an operator which takes similar jobs having the same requirement and groups them into batches.  It is the responsibility of the operator to sort jobs with similar needs.  Examples of Batch Operating Systems: Payroll Systems, Bank Statements, etc. 11  Types of OS: Multiprocessors  Multi-Processing Operating System is a type of Operating System in which more than one CPU is used for the execution of resources.  Also known as parallel systems, tightly-coupled systems  Advantages include: 1. Increased throughput 2. Economy of scale 3. Increased reliability: As it has several processors, so, if one processor fails, we can proceed with another processor.  Two types:  Asymmetric Multiprocessing – each processor is assigned a specie task (Sun's operating system SunOS Version 4 provided asymmetric multiprocessing).  Symmetric Multiprocessing – each processor performs all tasks (Version 5 (Solaris) is symmetric on thesame hardware). 12  Types of OS: Clustered Systems  Like multiprocessor systems, but multiple systems working together  Some cluster products support dozens of systems in a cluster, as well as clustered nodes that are separated by miles.  Usually sharing storage via a storage-area network (SAN)  Provides a high-availability service which survives failures  Asymmetric clustering has one machine in hot-standby mode  Symmetric clustering has multiple nodes running applications, monitoring each other 13  Types of OS: Multiprogramming Systems  Multiprogramming Operating Systems can be simply illustrated as more than one program is present in the main memory and any one of them can be kept in execution.  This is basically used for better execution of resources (efficiency). 14  Types of OS: Timesharing (Multitasking)  Each task is given some time to execute so that all the tasks work smoothly.  Each user gets the time of the CPU as they use a single system.  These systems are also known as Multitasking Systems.  Multitasking Operating System is simply a multiprogramming Operating System with having facility of a Round-Robin Scheduling Algorithm.  The time that each task gets to execute is called quantum.  After this time interval is over OS switches over to the next task. 15  Types of OS: Distributed Operating System  Various autonomous interconnected computers communicate with each other using a shared communication network.  Independent systems possess their own memory unit and CPU.  These are referred to as loosely coupled systems or distributed systems.  These systems’ processors differ in size and function.  The major benefit of working with these types of the operating system is that it is always possible that one user can access the files or software which are not actually present on his system but some other system connected within this network i.e., remote access is enabled within the devices connected in that network. 16  Types of OS: Network Operating System  These systems run on a server and provide the capability to manage data, users, groups, security, applications, and other networking functions.  These types of operating systems allow shared access to files, printers, security, applications, and other networking functions over a small private network. 17  Types of OS: Real-Time Operating System  The time interval required to process and respond to inputs is very small.  This time interval is called response time.  Real-time systems are used when there are time requirements that are very strict like missile systems, air traffic control systems, robots, etc.  Types of Real-Time Operating Systems:  Hard Real-Time Systems: 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 an accident.  Soft Real-Time Systems: These OSs are for applications where time- constraint is less strict. 18  Operating System Services  An operating system provides an environment for the execution of programs.  It provides certain services to programs and to the users of those programs. Figure 2.1 A view of operating system services. 19  …Operating-System Services  One set of operating-system services provides functions that are helpful to the user:  User interface- Almost all operating systems have a user interface (UI)  Varies between Command-Line (CLI), Graphics User Interface (GUI).  Program execution- The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error)  I/O operations- A running program may require I/O, which may involve a file or an I/O device  File-system manipulation- Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management.  Communications– Processes may exchange information, on the same computer or between computers over a network  Error detection– OS needs to be aware of possible errors and debug them. 20  …Operating-System Services  Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing:  Resource allocation- When multiple users or multiple jobs running concurrently, resources must be allocated to each of them  Many types of resources - Some (such as CPU cycles, main memory, and file storage) may have special allocation code, others (such as I/O devices) may have general request and release code  Accounting- To keep track of which users use how much and what kinds of computer resources  Protection and security- The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other  Protection involves ensuring that all access to system resources is controlled  Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts 21  System Calls  System calls provide the interface between a process and operating system.  System calls allow user-level processes to request services of the operating system.  Whenever a process needs to do something that only the OS can do – it performs a system call.  These calls are generally available as routines written in C and C++.  A number associated with each system call  System-call interface maintains a table indexed according to these numbers 22  Types of System Calls  System calls can be grouped roughly into five major categories: 1.Process control  end, abort  load, execute  create process, terminate process  get process attributes, set process attributes  wait for time  wait event, signal event  allocate and free memory 2.File management  create file, delete file  open, close  read, write, reposition  get file attributes, set file attributes 23  …Types of System Calls 3. Device management  request device, release device  read, write, reposition  get device attributes, set device attributes  logically attach or detach devices 4. Information maintenance  get time or date, set time or date  get system data, set system data  get process, file, or device attributes  set process, file, or device attributes 5. Communications  create, delete communication connection  send, receive messages  transfer status information  attach or detach remote devices 24  Examples of Windows and Unix System Calls 25  System Programs  “The one program running at all times on the computer” is the kernel.  Everything else is either a system program, or an application program.  System programs(system utilities), provide a convenient environment for program development and execution.  They can be divided into these categories: 1. File management (create, delete, copy, rename, print, dump, list, and generally manipulate files and directories). 2. Status information (Some ask the system for info - date, time, amount of available memory, disk space, number of users. Others provide detailed performance, logging) 3. File modification (Several text editors may be available to create and modify the content of files stored on disk or other storage devices). 4. Program loading and execution (Once a program is assembled or compiled, it must be loaded into memory to be executed). 5. Programming-language support (Compilers, assemblers, debuggers, and Interpreters). 26  …System Programs 6. Communications (creating virtual connections among processes, users, and computer systems. They allow users to send messages to one another’s screens, to browse Web pages, to send e-mail messages, to log in remotely, or to transfer files from one machine to another). 7. Background Services (running system-program processes are known as services, subsystems, or daemons).  Along with system programs, most operating systems are supplied with programs that are useful in solving common problems or performing common operations. Such application programs. 8. Application programs (include Web browsers, word processors and text formatters, spreadsheets, database systems, compilers, plotting and statistical- analysis packages, and games). 27  Operating-System Structure  A system as large and complex as a modern operating system must be engineered carefully if it is to function properly and be modified easily.  A common approach is to partition the task into small components, or modules, rather than have one monolithic system.  Each of these modules should be a well-defined portion of the system, with carefully defined inputs, outputs, and functions. 28  Operating-System Structure: Simple Structure  These systems started as small, simple, and limited systems and then grew beyond their original scope.  MS-DOS is an example of such a system. It was written to provide the most functionality in the least space, so it was not carefully divided into modules.  Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated, Figure 2.11 shows its structure. 29 Operating-System Structure: Monolithic Structure  Like MS-DOS, UNIX initially was limited by hardware functionality.  It consists of two separable parts: the kernel and the system programs.  The kernel provides the file system, CPU scheduling, memory management, and other operating-system functions through system calls. 30  Operating-System Structure: Layered Approach  The operating system is divided into a number of layers (levels), each built on top of lower layers.  The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.  Advantages:  Modularity simplifies development and debugging.  With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.  Disadvantages:  The major difficulty with the layered approach involves appropriately defining the various layers, because a layer can use only lower-level layers, careful planning is necessary. 31  Operating-System Structure: Microkernels  In the mid-1980s, researchers at Carnegie Mellon University developed an operating system called Mach that modularized the kernel using the microkernel approach.  Microkernel approach: minimal kernel, only essential components.  This method structures the operating system by removing all nonessential components from the kernel and implementing them as system and user-level programs → The result is a smaller kernel.  Advantages:  Easier to extend a microkernel (All new services are added to user space and consequently do not require modification of the kernel)  provides more security and reliability(less code is running in kernel mode since most services are running as user rather than kernel processes. If a service fails, the rest of the operating system remains untouched.)  Disadvantages:  Performance overhead of user space to kernel space communication. 32  …Operating-System Structure: Microkernels  The main function of the microkernel is to provide communication between the client program and the various services that are also running in user space.  Communication is provided through message passing, Figure 2.14 illustrates the architecture of a typical Microkernel. 33  Operating-System Structure: Modules  The best current methodology for operating-system design involves using loadable kernel modules.  Here, the kernel has a set of core components and links in additional services via modules, either at boot time or during run time.  Most modern operating systems implement kernel modules such as Solaris, Linux, and Mac OS X, as well as Windows.  Advantages:  The overall result resembles a layered system in that each kernel section has defined, protected interfaces; but it is more flexible than a layered system, because any module can call any other module.  The approach is also similar to the microkernel approach in that the primary module has only core functions and knowledge of how to load and communicate with other modules; but it is more efficient, because modules do not need to invoke message passing in order to communicate. 34  …Operating-System Structure: Modules  The Solaris operating system structure, shown in Figure 2.15, is organized around a core kernel with seven types of loadable kernel modules.  Linux also uses loadable kernel modules, primarily for supporting device drivers and file systems. 35  Operating-System Structure: Hybrid Systems  In practice, very few operating systems adopt a single, strictly defined structure.  Example of hybrid systems: Apple Mac OS X operating system and the two most prominent mobile operating systems, iOS and Android.  The Apple Mac OS X operating system uses a hybrid structure.  As shown in Figure 2.16, it is a layered system, the Kernel combines Mach microkernel and the BSD UNIX layers, other services provided by modules. 36 THANK YOU!