Operating System

Operating System Structures

(Perspectives)

·       Services provided by OS.

·       Interface by users and programmers

·        How Os disassembles the system to  components and connecting them?.

System Components

1.    Process

A program may contain more than one/many  processes

                      A process is a program in execution./Unit work of a system.

Every instruction execution is part of a process,

Ø Creating and deleting both user and system processes.

Ø Resource management

Ø Process synchronization

Ø Process communication

Ø Dead lock handling

2.    Main memory

Ø Main memory is the repository for data shared by cpu and i/o devices

Ø A program is to be allocated to absolute address(address in main memory) to be executed.

Ø Once program is completed execution memory should be freed , memory space is declared available.

Ø Instructions (lines of a program ) should be in main memory for the  fetching  by the  cpu. 

Ø OS should do the following

                1.Should track which parts of memory are currently being used

          2.Deciding which processes are to be loaded to memory when memory space become available.

          3. Allocating and deallocating memory space as needed.

3.    File management

Ø Files are collection of related information defined by its creator.

Ø Files consists of sequence of bytes and as records meaning defined by its creators. They usually are stored  in secondary storage and sometimes in primary memory.

Ø Os takes care of

ü  Creation &deletion of files

ü Creation &deletion of directories

ü Mapping files to secondary storage device.

ü Backing up of files.

4       I/O system management

Ø The i/o sub system(DMA etc) hides the details of i/o operation from OS

Ø I/o subsystem consists of component that manes buffering, caching  and spooling.

Ø It consists of device diver interface.

5       Secondary storage management

Ø Free space management

Ø Storage allocation

Ø Disk scheduling

6       Networking

Ø  Networking OS should taek care of many processors with individual memory.

Ø Protocols like FTP,NFS(remote login),HTTP

Are used

                                                 

7       Protection System

Ø Protection of resources ,processes from invalid users,other process’s activities etc.

8       Command-Interpreter System

Ø Commands are prewritten programs (user inter face of OS )i.e shell

System Programs

• File management:to create,delete ,copy,rename,print,dump,list and manipulate fules and directories
• Status information:informs system,time,memory usage,cpu usage etc
• File modification:Text editors which are capable of modifying content.
• Programming language support:Complilers,asseblers, and interpreters for common programming languages.
• Prgramloading and execution:Loadersmlinkage editors debuugers etc.
• Communications:emails,meassage passing systems :eg:talk,wall in Linux

System structure

            Resident monitor: Responsible for  editing tam ,flash memory etc.