Cs506 First lecture

Materials Lecture note ELearning web site : http://scholar.cu.edu.eg/?q=nermin-hamza/ Abraham Silberschatz, Peter B. Galvin, Greg Gagne , “Operating System Concepts” , 8th edition Paperback, 2010 Vijay Shukla “ operating systems”, S K Kataria & Sons, third edition 2011

Assessement Mid term 20% Lab or assignments 10% Final exam 70% -------------------------------------- Total 100%

Let’s start

Introduction The 1960’s definition of an operating system is “the software that controls the hardware”. An operating system is the set of programs that controls a computer. Some examples of: operating systems are UNIX, Mach, MS-DOS, MS-Windows, Windows/NT, Chicago, OS/2, MacOS, VMS, MVS, and VM.

Computer System Structure 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 Users People, machines, other computers

Four Components of a Computer System

What is Operating System The operating system comprises a set of software packages that can be used to manage interactions with the hardware. Kernel Shell

Components of the operating system The kernel: Portion of operating system that is in main memory which represents the operating system's basic functions such as management of memory, processes, files, main inputs/outputs and communication functionalities.

Components of the operating system The shell: allowing communication with the operating system via a control language, letting the user control the peripherals without knowing the characteristics of the hardware used, management of physical addresses, etc.

Objectives of Operating Systems To hide details of hardware by creating abstraction To allocate resources to processes (Manage resources) Provide a pleasant and effective user interface

System Components

System Components Even though, not all systems have the same structure many modern operating systems share the same goal of supporting the following types of system components

System Components Process Management Main-Memory Management File Management I/o Management Secondary-Storage Management Networking Protection System

System Components 1- Process Management a process is program in execution The five major activities of an operating system in regard to process management are: Creation and deletion of user and system processes. Suspension and resumption of processes. A mechanism for process synchronization. A mechanism for process communication. A mechanism for deadlock handling.

System Components 2- Main-Memory Management Main-Memory is a large array of words or bytes The major activities of an operating in regard to memory-management are: Keep track of which part of memory are currently being used and by whom. Decide which process are loaded into memory when memory space becomes available. Allocate and de-allocate memory space as needed.

System Components 3- File Management A file is a collected of related information defined by its creator. Computer can store files on the disk (secondary storage) The five main major activities of an operating system in regard to file management are The creation and deletion of files. The creation and deletion of directions. The support of primitives for manipulating files and directions. The mapping of files onto secondary storage. The back up of files on stable storage media

System Components 4- I/O System Management I/O subsystem hides the peculiarities of specific hardware devices from the user.

System Components 5- Secondary-Storage Management Secondary storage consists of tapes, disks, and other media. The three major activities of an operating system in regard to secondary storage management are: Managing the free space available on the secondary-storage device. Allocation of storage space when new files have to be written. Scheduling the requests for memory access.

System Components 6- Networking A distributed systems is a collection of processors that do not share memory, peripheral devices, or a clock. The processors communicate with one another through communication lines called network. The communication-network design must consider routing and connection strategies, and the problems of contention and security.

System Components 7- Protection System Protection refers to mechanism for controlling the access of programs, processes, or users to the resources defined by a computer system

System Components 8- Command Interpreter System is an interface of the operating system with the user The main function of a command interpreter is to get and execute the next user specified command

Operating Systems Services

Operating Systems Services Program Execution allow the user to execute programs I/O Operations operating systems by providing I/O makes it convenient for the users to run programs File System Manipulation The output of a program may need to be written into new files or input taken from some files.

Operating Systems Services Communications It may be between processes running on the same computer or running on the different computers. Error Detection Error is one part of the system may cause malfunctioning of the complete system.

Computer-System Operation

Computer-System Operation A general-purpose computer system consists of a CPU and a number of device controllers that are connected through a common bus that provides access to the shared memory.

Computer-System Operation Device controller for every device: Each device controller is in charge of a specific type ofdevice. Depending on the controller more than one evice may be attached. Device driver in O.S. for every device for interface. It loads the appropriate registers within the device controller.

Computer-System Operation: Difference between a device controller and a device driver? The Controller is a piece of hardware that lets the computer's motherboard communicate with device The driver is a piece of software that tells the operating system how to communicate with a specific bit computer hardware.

Computer-System Operation: initial program For a computer to start running—for instance, when it is powered up or rebooted—it needs to have an initial program to run.

Computer System Organization: How operating System takes control? Power on self test(POST) Bios Sector Boot Sector Configuration Files Loading

Computer System Organization: How operating System takes control? POST: in this step the computer checks itself to see if the basic devices(keyboard, mouse, video etc..) are connected with the processor . It sends predefined signals to these devices and expects pre-defined responses back from these devices. BIOS : (basic input output system): part of ROM and perform checking the memory system.

Computer System Organization: How operating System takes control? Boot Sector Reading: BIOS reads the disk sector where files are needed to start the operating system. The area of the disk where there files are located is called Boot Sector. Once these files are loaded , few more configuration files are also required which contains what to do upon the start of computer

Computer System Organization: How operating System takes control? Bootstrap : is a technique by which a simple computer program activates a more complicated system of programs.

Computer System Organization: How operating System takes control? 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

Special-Purpose Systems

Special-Purpose Systems Real-Time Embedded Systems General-purpose computers, running standard operating systems—such as UNIX— Special-purpose applications are hardware devices with a special-purpose embedded operating system providing just the functionality desired A real-time system is used when rigid time requirements have been placed on the operation of a processor or the flow of data control devices in a dedicated application or Sensors bring data to the computer. A real-time system functions correctly only if it returns the correct result within its time constraints

Special-Purpose Systems Multimedia Systems operating systems are designed to handle conventional data such as text files. Multimedia data consist of audio and video files as well as conventional files. Multimedia application often includes a combination of both

Special-Purpose Systems Handheld Systems Handheld systems include personal digital assistants (PDAs), such as Palm and Pocket-PCs, and cellular telephones. many of which use special-purpose embedded operating systems.

Special-Purpose Systems Open-Source Operating Systems Open-source operating systems are those made available in source-code format rather than as compiled binary code. Linux is the most famous open- source operating system, while Microsoft Windows is a well-known example of the opposite closed source approach benefits to open-source operating systems, including a community of interested (and usually unpaid) programmers who contribute to the code by helping to debug it, analyze it, provide support, and suggest changes. more secure than closed-source code