Operating System Concepts PDF

Dr. Arwa E. Abulwafa  Operating System Concepts  File System Interface  File System Implementation  Secondary Storage Structure  Threading  Process Management  CPU Scheduling  Memory Management  Virtual Memory 2  Computer Users  The users who use the overall computer sy...

Dr. Arwa E. Abulwafa  Operating System Concepts  File System Interface  File System Implementation  Secondary Storage Structure  Threading  Process Management  CPU Scheduling  Memory Management  Virtual Memory 2  Computer Users  The users who use the overall computer system.  Application Software  The software which users use directly to perform different activities.  This software is simple and easy to use like Browsers, Word, Excel, different Editors, Games etc. These are usually written in high-level languages, such as Python, Java and C++. 3  System Software  The software which is more complex in nature and they are more near to computer hardware.  These software are usually written in low-level languages like assembly language and includes Operating Systems (Microsoft Windows, macOS, and Linux), Compiler, and Assembler etc.  Computer Hardware  includes Monitor, Keyboard, CPU, Disks, Memory, etc. 4 5  So now let's put it in simple words:  If we consider a Computer Hardware is body of the Computer System, then we can say an Operating System is its soul which brings it alive i.e. operational.  We can never use a Computer System if it does not have an Operating System installed on it. 6  Application programs are programs that are developed for end-users.  These programs provide an application to the end- user and hence used by them.  They are loaded into the system according to the needs of the user.  Examples: web browsers, Email, gaming, etc. 7 8 9 10 11 12  Input Units:  Used to enter the data from the outside world into the primary storage as the input through input devices.  The input devices are the medium of communication between the outside world and the computer system.  Output Units:  The output devices produce or generate the desired result according to our input, such as a printer, monitor, etc. 13  Main Memory:  The Random Access Memory is the main memory of the computer system, which is known as RAM.  The main memory can store the operating system software, application software, and other information.  The Ram is one of the fastest memory, and it allows the data to be readable and writeable. 14  Secondary memory  Used to store the data and programs on a long-term basis in the secondary memory.  The hard disks and the optical disks are the common secondary devices.  It is slow and cheap memory as compare to primary memory.  This memory is not connected to the processor directly. 15  Processor  The processor is an electric circuitry within the computer system.  The Central processing unit is the central processor or main processor of the computer system.  The processor carries out the instructions of the computer program with the help of basic arithmetic and logic, input/output operations. 16  Control Unit  The control unit (CU) controls all the activities or operations which are performed inside the computer system.  It receives instructions or information directly from the main memory of the computer. 17  Arithmetic and Logical Unit (ALU)  The arithmetic and logical unit is the combinational digital electronic circuit that can perform arithmetic operations on integer binary numbers.  It presents the arithmetic and logical operation.  The outputs of ALU will change asynchronously in response to the input.  The basic arithmetic and bitwise logic functions are supported by ALU. 18  Storage Unit  The information or set of guidelines are stored in the storage unit of the computer system.  The storage unit provides the space to store the data or instruction of processed data.  The information or data is saved or hold in computer memory or storage device.  The data storage is the core function and fundamental of the computer components. 19  Primary storage is also known as the main memory and is the memory directly accessible by the CPU.  Some primary storage devices are:  ROM  ROM is read only memory.  This memory cannot be changed, it can only be read as required.  Since ROM is unchangeable memory, it is used by data and programs that are frequently required and seldom changed, like the system boot program. 20  Primary storage is also known as the main memory and is the memory directly accessible by the CPU.  Some primary storage devices are:  ROM  ROM is read only memory.  This memory cannot be changed, it can only be read as required.  Since ROM is unchangeable memory, it is used by data and programs that are frequently required and seldom changed, like the system boot program. 21  RAM  RAM is random access memory.  It is volatile i.e. the data in RAM is lost when the power is switched off.  RAM is the major form of primary memory as it is quite fast.  However, it is also quite expensive. 22  Cache Memory  Cache is used to store data and instructions that are frequently required by the CPU so it doesn't have to search them in the main memory.  This is a small memory that is also very fast. 23  Secondary or external storage is not directly accessible by the CPU.  The data from secondary storage needs to be brought into the primary storage before the CPU can use it.  Secondary storage contains a large amount of data permanently. 24 25  The different types of secondary storage devices:  Hard Disk  Hard disks are the most famously used secondary storage devices.  They are round, flat pieces of metal covered with magnetic oxide.  They are available in many sizes ranging from 1 to 14 inch diameter. 26  Floppy Disk  They are flexible plastic discs which can bend, coated with magnetic oxide and are covered with a plastic cover to provide protection.  Floppy disks are also known as floppies and diskettes. 27  Memory Card  This has similar functionality to a flash drive but is in a card shape.  It can easily plug into a port and removed after its work is done.  A memory card is available in various sizes such as 8MB, 16MB, 64MB, 128MB, 256MB etc. 28  Flash Drive  This is also known as a pen drive.  It helps in easy transportation of data from one system to another.  A pen drive is quite compact and comes with various features and designs. 29  CD-ROM  This is short for compact disk - read only memory.  A CD is a shiny metal disk of silver color.  It is already pre recorded and the data on it cannot be altered.  It usually has a storage capacity of 700 MB. 30  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. 31  Convenient to use:  One of the objectives is to make the computer system more convenient to use in an efficient manner.  User Friendly:  To make the computer system more interactive with a more convenient interface for the users.  Easy Access:  To provide easy access to users for using resources by acting as an intermediary between the hardware and its users. 32  Management of Resources:  For managing the resources of a computer in a better and faster way.  Controls and Monitoring:  By keeping track of who is using which resource, granting resource requests, and mediating conflicting requests from different programs and users.  Fair Sharing of Resources:  Providing efficient and fair sharing of resources between the users and programs. 33  Spooling (Simultaneous Peripheral Operation On-Line):  This is a device management technique used for processing different tasks on the same input/output device.  When there are various users on a network sharing the same resource then it can be a possibility that more than one user might give it a command at the same point in time.  So, the operating system temporarily stores the data of every user on the hard disk of the computer to which the resource is attached. 34  The individual user need not wait for the execution process to be completed.  Instead, the operating system sends the data from the hard disk to the resource one by one.  It is a way to process data serially.  Example: printer 35  There are several types of Operating Systems 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 36  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. 37 38  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. 39  It is a type of Operating System in which more than one CPU is used for the execution of resources.  It betters the throughput of the System. 40  Multitasking Operating System is simply a multiprogramming Operating System with having facility of a Round-Robin Scheduling Algorithm.  It can run multiple programs simultaneously.  There are two types of Multi-Tasking Systems which are listed below.  Preemptive Multi-Tasking  Cooperative Multi-Tasking 41 42  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.  The task can be from a single user or different users also. 43  The time that each task gets to execute is called quantum.  After this time interval is over OS switches over to the next task.  Examples:  IBM VM/CMS  TSO (Time Sharing Option)  Windows Terminal Services 44 45  These types of operating system is a recent advancement in the world of computer technology and are being widely accepted all over the world and, that too, at a great pace.  Various autonomous interconnected computers communicate with each other using a shared communication network. 46  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. 47  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.  Examples:  LOCUS, etc. 48 49  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. 50  One more important aspect of Network Operating Systems is  that all the users are well aware of the underlying configuration, of all other users within the network, their individual connections, etc. and that’s why these computers are popularly known as tightly coupled systems.  Examples:  Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, BSD, etc. 51 52  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.  Real-time systems are used when there are time requirements that are very strict like missile systems, air traffic control systems, robots, etc. 53  Hard Real-Time Systems:  Hard Real-Time 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. Virtual memory is rarely found in these systems. 54  Soft Real-Time Systems:  These OSs are for applications where time-constraint is less strict. 55  Examples:  Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc. 56  To brief, Following are some of important functions of an operating System which we will look in more detail in upcoming chapters:  Process Management  I/O Device Management  File Management  Network Management  Main Memory Management 57  Secondary Storage Management  Security Management  Command Interpreter System  Control over system performance  Job Accounting  Error Detection and Correction  Coordination between other software and users  Many more other important tasks 58  It is a program introduced by the company that produce the hardware  so that the operating system can communicate with the hardware. 59  The major categories of Programming Languages:  Machine Language  Assembly Language  High Level Language  System Language  Scripting Language 60  Machine Language or Code  This is the language that is written for the computer hardware.  Such language is effected directly by the central processing unit (CPU) of a computer system. 61  Assembly Language  It is a language of an encoding of machine code that makes simpler and readable. 62  High Level Language  The high level language is simple and easy to understand and it is similar to English language.  For example, COBOL, FORTRAN, BASIC, C, C+, Python, etc.  High-level languages are very important, as they help in developing complex software. 63  Although a high-level language has many benefits, yet it also has a drawback.  It has poor control on machine/hardware. 64 Compiler Interpreter  Compiled code run faster  Interpreted code run slower  Compiler displays all errors and  The interpreter reads a single warning at the compilation time; statement and shows the error if Therefore, you can’t run the any; therefore you must correct program without fixing errors the error to interpret next line.  It takes an entire program  It takes a single line of code.  It generates intermediate  It never generate any machine code. intermediate machine code.  Display all errors after  Displays all errors of each line compilation, all at the same time. one by one.  C, C++, C#, Scala, Java.  PHP, Perl, Ruby. 65  Input Source Target Compiler Program Program Error messages Output Source Program Interpreter Output Input Error messages 66 Interpreter 67 Compiler 68  There are plenty of Operating Systems available in the market which include paid and unpaid (Open Source).  Following are the examples of the few most popular Operating Systems: 69  Windows:  This is one of the most popular and commercial operating systems developed and marketed by Microsoft.  It has different versions in the market like Windows 8, Windows 10 etc and most of them are paid. 70  Linux  This is a Unix based and the most loved operating system first released on September 17, 1991 by Linus Torvalds.  Today, it has 30+ variants available like Fedora, OpenSUSE, CentOS, UBuntu etc.  Most of them are available free of charges though you can have their enterprise versions by paying a nominal license fee. 71  MacOS  This is again a kind of Unix operating system developed and marketed by Apple Inc. since 2001.  iOS  This is a mobile operating system created and developed by Apple Inc. exclusively for its mobile devices like iPhone and iPad etc. 72  Android  This is a mobile Operating System based on a modified version of the Linux kernel and other open source software, designed primarily for touchscreen mobile devices such as smartphones and tablets.  Some other old but popular Operating Systems include Solaris, VMS, OS/400, AIX, z/OS, etc. 73  Operating systems have been evolving through the years.  In the 1950s, computers were limited to running one program at a time like a calculator,  but later in the following decades, computers began to include more and more software programs, sometimes called libraries, that formed the basis for today’s operating systems. 74  The first Operating System was created by General Motors in 1956 to run a single IBM mainframe computer, its name was the IBM 704.  IBM was the first computer manufacturer to develop operating systems and distribute them in its computers in the 1960s. 75  There are few facts about Operating System evaluation:  Stanford Research Institute developed the oN-Line System (NLS) in the late 1960s,  which was the first operating system that resembled the desktop operating system we use today.  Microsoft bought QDOS (Quick and Dirty Operating System) in 1981 and branded it as Microsoft Operating System (MS-DOS).  As of 1994, Microsoft had stopped supporting MS-DOS. 76  Unixwas developed in the mid-1960s by the Massachusetts Institute of Technology,  AT&T Bell Labs, and General Electric as a joint effort. Initially it was named MULTICS, which stands for Multiplexed Operating and Computing System.  FreeBSD is also a popular UNIX derivative, originating from the BSD project at Berkeley.  All modern Macintosh computers run a modified version of FreeBSD (OS X). 77  Windows 95 is a consumer-oriented graphical user interface-based operating system built on top of MS- DOS.  It was released on August 24, 1995 by Microsoft as part of its Windows 9x family of operating systems.  Solaris is a proprietary Unix operating system originally developed by Sun Microsystems in 1991.  After the Sun acquisition by Oracle in 2010 it was renamed Oracle Solaris. 78 79