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

SLC/Ver1.0/OS CONCEPTS/Oct'991

INTRODUCTIONINTRODUCTION

• What is an Operating System?

• Operating Structure-System Components-OS Services-System Calls & Programs-System Structure-Virtual Machines


What is an OS?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



COMPUTERHARDWARE

APPLICATION PROGRAMS

COMPILER

USER1

USER2

USERN

ASSEMBLER DATABASESYSTEM

OPERATING SYSTEM


What is An OS?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.



• 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.


Operating System StructureOperating 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.


System ComponentsSystem Components

• Process Management

• Main-Memory Management

• File Management

• I/O System Management

• Secondary-Storage Management

• Networking


System ComponentsSystem Components

• Protection System

• Command-Interpreter System


Process ManagementProcess 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.


Process ManagementProcess 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.


Main-Memory ManagementMain-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.



• Keep several programs in memory.

• There are many different memory-management scheme.



• 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.


File ManagementFile 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.


File ManagementFile 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.


I/O System ManagementI/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.


Secondary-Storage ManagementSecondary-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.


Secondary-Storage ManagementSecondary-Storage Management

• The OS responsibility:-Free-space management.-Storage allocation.-Disk scheduling.1


NetworkingNetworking

• Processors communicate with one another through various communication lines.

• The processors in the system are connected through a communication network.


Protection SystemProtection 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.


Command-Interpreter SystemCommand-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.


Operating System ServicesOperating System Services

• Types of services-Program Execution.-I/O operations-File-System manipulation-Communications-Error detection-Resource allocation


Operating System ServicesOperating System Services

• Types of services-Accounting-Protection


System CallsSystem 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.


System CallsSystem Calls

• System calls can be roughly grouped into five major categories:-process control,-file manipulation-device manipulation-information maintenance-communication


System Calls-Process ControlSystem 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


System Calls-File ManipulationSystem Calls-File Manipulation

• Create file, delete file

• open, close

• read, write, reposition

• get file attributes, set file attributes


System Calls-Device ManipulationSystem Calls-Device Manipulation

• request device, release device

• read, write, reposition

• get device attributes, set device attributes

• logically attach or detach devices


System Calls-Information System Calls-Information MaintenanceMaintenance

• get time or date, set time or date

• get system date, set system date


System Calls-CommunicationsSystem Calls-Communications

• create, delete communication connection

• send, receive message

• transfer status information

• attach or detach remote devices


System ProgramsSystem Programs

• It is a logical layer just above OS.

• System programs provide a more convenient environment for program development and execution.



• They can be divided into several categories:-File Manipulation-Status information-File Modification-Programming Language Support



• 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.


System StructureSystem Structure

• A common approach is to partition the task into small components, rather than have one monolithic system.


System Structure-Simple System Structure-Simple StructureStructure

• 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


System Structure-Simple System Structure-Simple StructureStructure

Application program

Resident system program

MS-DOS device driver

ROM BIOS device drivers

MS-DOS Layer structure


System Structure-Layered System Structure-Layered ApproachApproach

• 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.


System Structure-Layered System Structure-Layered ApproachApproach

Layer M-1

An OS Layer

Layer M


Virtual MachinesVirtual 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.

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