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
Conventional O.S. System Architecture
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 (The main
Objectives)

• 1) Make the peripheral device interface
  Hardware functional/ operational via Device
  Driver Programs.
• 2) Implement Data Transfer Protocols between
  the CPU/Memory combine and the Device Interfaces.
  
• The commonly used Peripherals
• Key board Character Oriented Device.
• Mouse Click Character Oriented Device.
• V.D.U. Display Block Oriented Device.
• Disk (Magnetic CD/ DVD ) Flash Memory.
• Block Oriented Devices.
• Printers (Impact Non Impact) Block /
  Character Oriented .

8
Management of Peripheral Devices (The Tasks
Performed)

• 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 through well defined
• Data Transfer Protocols between the
  two .
• 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.

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
Data Transfer Protocols

• All types of Data Transfer takes place via the
  Device Interface through I/O Bus.
• Mainly the following types of Data Transfer /
  Interface Protocols are in use
• Polling Programmed
• Interrupt Driven Programmed .
• Direct Memory Access (DMA) Non Programmed .
• Plug Play Normally a Default Mode supported
  by most modern Operating Systems can either be
  Interrupt Driven and/or DMA based .

11
File Organizations

• Tree Like Structure Directory acts as Index
• Root Directory
• Sub Directory 1 Sub Directory 2
  Sub Directory n
• File 1 .. File n File 1 .. File m
  File 1 .. File k
• Each file is associated with access control
  Read / Write / Execute

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Various File Media and the Corresponding
Protocols

• Fixed Magnetic Disk Hard ( Internal) Direct
  Drive Mechanism DMA / Interrupt based Data
  Transfer.
• Removable Magnetic Disk ( External) Direct
  Drive Mechanism , DMA / Interrupt protocols are
  used.
• Removable Optical Disks Direct Drive mainly DMA
  based.
• Removable Flash Drives Random access,
  Electronic Interrupt based.
• Magnetic Tape Sequential Interrupt based.

13
File Management Functions

• 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.

14
The Typical Memory Hierarchy

Electronic Mostly Volatile
GPRs
SIZE
On Chip CACHE
COST SPEED
Off Chip Cache
Main/ Primary / Physical Memory
Fixed Secondary Memory Magnetic Disk Non
Volatile
Removable Secondary Mag.Tapes, Electronic
Flash, Optical CD_ROM, DVDs Non Volatile
15
Memory Hierarchy ( Various Levels)

• 1. CPU Registers General Purpose Registers
  are accessible to ALL ,
• cannot be protected from any of the User
  Programs and/or 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, DVDs, Tapes, Flash ( To provide virtual
  storage / Memory also acts as Filing Cabinets )
  Highest Size, Lowest Speed Cost/bit .

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Memory Management Objectives

• Keeping track of memory occupancy at any level.
• (which process resides where at each level
  of the Memory Hierarchy and how much of
  memory it occupies at each of these levels).
• Swapping in / out portions of any process
  between any two adjacent levels on requirement.
  Allocation / Replacement Policy.
• Ensure availability of enough memory to any
  requesting process at each of these Hierarchical
  Levels in a manner transparent to that process.
• Create the feeling of the existence of an
  infinite sized , high speed memory for any user
  process Virtual Memory . This requires close
  interface with the File System.

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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
  / Several Cores in a Multi Core System which may
  be
• a) Tightly Coupled ( Sharing most of
  the Memory Hierarchy under the control of a
  centralized O.S.) Contemporary Dual Core
  Hyper-Threading
• b) Loosely Coupled. (Distributed/
  Networked).

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Processor Management Tasks - 2

• Allocate / De-allocate jobs/tasks / processes
  to the available processor(s) / core(s) (in
  accordance with predefined policy).
• Keep track of current status of each process
  Ready, Running, Waiting as well as the
  processor(s) / core(s) Busy , Free .
• Decide on the Time Quantum allotted to each
  process on any available processor/core Time
  Sharing System .
• Changing execution modes of each processor/core
  User / Kernel.
• Ensure guaranteed response time to each
  process.
• Report any illegal operation(s) / exception
  and take corrective
• actions.

19
Evolution of Operating System

• Serial .
• Simple Batch.
• Multi programmed Batch.
• The Process Thread Concepts.
• Time Shared Uni- Processor System
• - Multi Tasking.
• Time Shared Multi Processor / Multi Core System
  
• - Multi Threading.
• - Super Threading Hyper
  Threading.