SLC/Ver1.0/OS CONCEPTS/Oct'991INTRODUCTION What is an Operating System? Operating Structure -System Components -OS Services -System Calls & Programs -System Structure -Virtual Machines

SLC/Ver1.0/OS CONCEPTS/Oct'992 What is an OS? Important part of almost every computer system. Computer System can be divided roughly into four components -The hardware -The Operating System -The Application Program -The User

SLC/Ver1.0/OS CONCEPTS/Oct'993 What is an OS? COMPUTER HARDWARE APPLICATION PROGRAMS COMPILER USER 1 USER 2 USER N ASSEMBLER DATABASE SYSTEM OPERATING SYSTEM

SLC/Ver1.0/OS CONCEPTS/Oct'994 What is An OS? An Operating System is similar to a government. We can view an Operating Systems as a resource allocator. An Operating System is a control program.

SLC/Ver1.0/OS CONCEPTS/Oct'995 What is an OS? No adequate definition of an OS. Fundamental Goal of Computer System is to execute user programs and to make solving user problems easier. The OS is the one program running at all times on the computer, with all else being application programs.

SLC/Ver1.0/OS CONCEPTS/Oct'996 Operating System Structure There are several vantage points from which to view an OS -by examining the services it provides. -another by looking at the interface. -by disassembling the system into its components and their interconnections.

SLC/Ver1.0/OS CONCEPTS/Oct'997 System Components Process Management Main-Memory Management File Management I/O System Management Secondary-Storage Management Networking

SLC/Ver1.0/OS CONCEPTS/Oct'998 System Components Protection System Command-Interpreter System

SLC/Ver1.0/OS CONCEPTS/Oct'999 Process Management A process can be thought of as a program in execution. A process needs certain resources. A process is the unit of work in the system.

SLC/Ver1.0/OS CONCEPTS/Oct'9910 Process Management The OS responsibility in connection with process management -Creation and deletion of both user and system processes -The suspension and resumption of processes -The provision of mechanism for process synchronization, process communication.

SLC/Ver1.0/OS CONCEPTS/Oct'9911 Main-Memory Management It is a large array of words or bytes. Main-memory is a repository of quickly accessible data shared by CPU and I/O devices. The main-memory is generally the only large storage device that the CPU is able to address and access directly.

SLC/Ver1.0/OS CONCEPTS/Oct'9912 Main-Memory Management Keep several programs in memory. There are many different memory- management scheme.

SLC/Ver1.0/OS CONCEPTS/Oct'9913 Main-Memory Management The OS responsibility in connection with memory management -Keep track of memory. -Which processes are to be loaded. -Allocate and deallocate memory space as needed.

SLC/Ver1.0/OS CONCEPTS/Oct'9914 File Management File Management is one of the most visible components of an Operating System. The OS abstracts from the physical properties of its storage devices to define a logical storage unit, the file.

SLC/Ver1.0/OS CONCEPTS/Oct'9915 File Management File is a collection of related information defined by its creator. The OS responsibility -The creation and deletion of files. -The Support for manipulating files. -The mapping of files onto secondary storage.

SLC/Ver1.0/OS CONCEPTS/Oct'9916 I/O System Management One of the purpose of an OS is to hide the peculiarities of specific h/w devices from the user. I/O subsystem consists of -A memory management components -A general device-driver Interface -Drivers for specific hardware devices.

SLC/Ver1.0/OS CONCEPTS/Oct'9917 Secondary-Storage Management Main-Memory is to small and volatile. Computer system must provide secondary storage to back up main memory. Computer system uses disks as the principle on-line storage medium, for both programs and data.

SLC/Ver1.0/OS CONCEPTS/Oct'9918 Secondary-Storage Management The OS responsibility: -Free-space management. -Storage allocation. -Disk scheduling.1

SLC/Ver1.0/OS CONCEPTS/Oct'9919Networking Processors communicate with one another through various communication lines. The processors in the system are connected through a communication network.

SLC/Ver1.0/OS CONCEPTS/Oct'9920 Protection System Protection refers to a mechanism for controlling the access of programs, processes, or users to the resources defined by a Computer System. E.g. memory-addressing hardware.

SLC/Ver1.0/OS CONCEPTS/Oct'9921 Command-Interpreter System Command-Interpreter is the interface between the user and the OS. A program that reads and interprets control statements is executed automatically. This program is called command- interpreter, and is often known as shell.

SLC/Ver1.0/OS CONCEPTS/Oct'9922 Operating System Services Types of services -Program Execution. -I/O operations -File-System manipulation -Communications -Error detection -Resource allocation

SLC/Ver1.0/OS CONCEPTS/Oct'9923 Operating System Services Types of services -Accounting -Protection

SLC/Ver1.0/OS CONCEPTS/Oct'9924 System Calls System calls provide the interface between a process and the OS. Some system may allow system calls to be made directly from a higher-level language program. E.G. To read data from a file and to copy them to another file.

SLC/Ver1.0/OS CONCEPTS/Oct'9925 System Calls System calls can be roughly grouped into five major categories: -process control, -file manipulation -device manipulation -information maintenance -communication

SLC/Ver1.0/OS CONCEPTS/Oct'9926 System Calls-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

SLC/Ver1.0/OS CONCEPTS/Oct'9927 System Calls-File Manipulation Create file, delete file open, close read, write, reposition get file attributes, set file attributes

SLC/Ver1.0/OS CONCEPTS/Oct'9928 System Calls-Device Manipulation request device, release device read, write, reposition get device attributes, set device attributes logically attach or detach devices

SLC/Ver1.0/OS CONCEPTS/Oct'9929 System Calls-Information Maintenance get time or date, set time or date get system date, set system date

SLC/Ver1.0/OS CONCEPTS/Oct'9930 System Calls-Communications create, delete communication connection send, receive message transfer status information attach or detach remote devices

SLC/Ver1.0/OS CONCEPTS/Oct'9931 System Programs It is a logical layer just above OS. System programs provide a more convenient environment for program development and execution.

SLC/Ver1.0/OS CONCEPTS/Oct'9932 System Programs They can be divided into several categories: -File Manipulation -Status information -File Modification -Programming Language Support

SLC/Ver1.0/OS CONCEPTS/Oct'9933 System Programs They can be divided into several categories: -Program loading and Execution -Communications -Application programs Perhaps the most important system program for an OS is command interpreter.

SLC/Ver1.0/OS CONCEPTS/Oct'9934 System Structure A common approach is to partition the task into small components, rather than have one monolithic system.

SLC/Ver1.0/OS CONCEPTS/Oct'9935 System Structure-Simple Structure Commercial system doesn’t have a well- defined structure. Such OS started as small, simple and limited systems, and then grew beyond their original scope. MS-DOS is an example of such a system

SLC/Ver1.0/OS CONCEPTS/Oct'9936 System Structure-Simple Structure Application program Resident system program MS-DOS device driver ROM BIOS device drivers MS-DOS Layer structure

SLC/Ver1.0/OS CONCEPTS/Oct'9937 System Structure-Layered Approach Consists of breaking the OS into a number of layers, each built on top of lower layers. The bottom layer is the hardware; the highest(layer N) is the user interface.

SLC/Ver1.0/OS CONCEPTS/Oct'9938 System Structure-Layered Approach Layer M-1 An OS Layer Layer M

SLC/Ver1.0/OS CONCEPTS/Oct'9939 Virtual Machines Virtual Machine creates a machine for each “user” and the user can choose which OS to run on that virtual machine e.g Java Virtual Machine.