Role of an Operating System Different Viewpoints

1
Role of an Operating System(Different Viewpoints)

• General Views.
• Users Views.
• System Designers Views.

2
Role of an Operating System (General Views)

• A piece of Software that helps a computer system
  to operate ( A System Software) all the time.
• The Monitor program that monitors all activities
  going on inside the Computer all the time.
• Any O.S. MUST be running always following Power
  On followed by boot up till the system is shut
  down.
• Any O.S. acts as a resource Manager. A resource
  implies anything that is needed for any user
  program to complete execution.
• Provides the very first level of any Man
  Machine Interface.

3
Role of an Operating System (Users View)

• Accepts commands that make a Computer
  act/operate (Input, Store, Process, Output) all
  the time.
• Shields the basic limitations of the Computers
  resources i.e. remove machine dependence of any
  user.
• Guarantees Response time for each user command.
• Provides a hospitable user friendly interface.

4
Role of an Operating System(System Designers
View) - 1

• Provides activates various utility services
  like Editors , Translators other Applications.
• Performs effective utilization management of
  all System Resources like Peripherals, CPU
  Memory thereby providing a Hardware Independent
  work bench/ platform.
• Presents an user interface ( Ideally should be
  Self explanatory Self Correcting) .

5
The O.S. System Hierarchy
Command Line Interpreter
Command Line Interpreter
Core / Device Drivers
GUI
H/W
E D I T O R
Graphics User Interface (GUI)
User Programs
6
Resource Management Tasks of any Operating System

• Management of Peripheral Devices .
• File System Support.
• Memory Management.
• Processor Management.

7
Management of Peripheral Devices

• Installation of device drivers / setting up
  the Invocation /
• Entry Points ( Interrupt Vectors).
• Invoking device driver programs on demand
  (usually user request
• via System Call / Software
  Interrupt).
• Allowing the fast paced CPU and the slow paced
  / faster
• peripherals to operate at their own
  speed.
• Guaranteeing availability of peripherals to all
  requesting
• processes without sacrificing
  response time.
• Enforce proper device sharing protocols if
  needed (to make non
• shareable devices shareable in a Time
  multiplexed fashion ).
• Monitoring each active device status.

8
The Device Driver Programs / Device Drivers

• Makes the peripheral device interfaces
  functional.
• Role of the Interfaces
• a) Matching Electrical Characteristics.
• b) Matching Speeds.
• The basic devices that should Operate
• Key board Read.
• Mouse Click.
• V.D.U. Display.
• Disk (Magnetic CD/ DVD ) Read Write.
• Printers (Impact Non Impact).

9
Basic Features of Device Drivers

• Makes the peripheral interfaces interact with
  the CPU in accordance with O.S. Commands.
• Written using Low Level / Low level Features of
  a programming language.
• Normally Underlying machine / CPU dependent.
• Employs privileged / supervisor mode
  Instructions.
• Contained in non-volatile ROMs and / or loaded
  from disk(s) on demand (if installed).

10
The File System

• Mostly used FUNCTION. This involves the
  following tasks
• Keeping track of the Secondary Stores (File
  Cabinet) .
• (which file stored where the directory
  structure)
• Storage / (Allocating space) for files.
  space
• De-allocating space for deleted files .
  management
• Compacting freed space on Magnetic disks.
• Accessibility control protection (Read,
  Write, Execute Access) of files.
• Forms the backbone of any Data Base and / or
  Information System.

11
Memory Management ( The Job at HAND)

• The Typical Modern Day Memory Hierarchy
• 1. CPU Registers General Purpose Registers
  are accessible to ALL , the User, System Programs
  like O.S. Compiler
• Smallest, Fastest Most Costly (Cost /
  bit )
• 2. Cache (ON Chip OFF Chip) ( High
  Speed Window of Main Memory . Helps to achieve
  Compatibility between High Speed , wider bit
  width CPU and low speed , lower bit width Memory
  Bus )
• Smaller, Less Cost/bit compared to
  registers, normally handled by Architecture
  Partly content addressable Static
• 3. Main or Primary Memory. Expandable NOT
  related to CPU width normally managed by the O.S.
  supported by Architectures MMU. Acts as the
  universal storage. Static Dynamic
• 4. Secondary Memory Disk (Hard,Floppy)
  / CDs /Tape ( To provide virtual storage /
  Memory ) Highest Size, Lowest Speed Cost/bit
  .

12
Memory Management Objectives

• Keeping track of main memory occupancy.
• (which process resides where in the
  main memory
• and how much main memory it
  occupies)
• Swapping in / out portions of any process
  between main memory secondary storage Disk
  Swap Space
• on requirement.
• Ensure availability of enough main memory in a
  manner transparent to each concerned process.
• Create the feeling of the existence of an
  infinite sized ,
• high speed memory for any user.

13
Processor Management Tasks - 1

• 1) In an Uni-Processor System, it involves
  managing the single CPU and its co-processors
  like Floating Point Units (FPUs) Multi Media
  (MMX), Memory Management Units (MMUs ) Normally
  handled directly by Architecture.
• 2) Coordinating Several CPUs in a Multiprocessor
  System which may be
• a) Tightly Coupled ( Sharing Main
  Memory
• under the control of a
  centralized O.S.).
• b) Loosely Coupled. (Distributed/
  Networked).

14
Processor Management Tasks - 2

• Allocate / De-allocate jobs/tasks / processes
  to the available processor(s)(in accordance with
  predefined policy).
• Keep track of current status of each process
• as well as the processor(s) .
• Decide on each of the processor(s) occupancy
  period(s).
• Ensure guaranteed response time to each
  process.
• Report any illegal operation(s) and take
  corrective
• actions.

15
Evolution of Operating System

• Serial .
• Simple Batch.
• Multi programmed Batch.
• The Process Thread Concepts.
• Time Sharing of Uni- Processor System
• - Multi Tasking.
• - Multi Threading.
• - Super Threading Hyper
  Threading.
• Multi Processing ( Parallel Distributed).