What is an Operating System O'S' Different Viewpoints

1
What is an Operating System O.S.
?(Different Viewpoints)

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

2
The Operating System O.S. (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
The Operating System O.S.(Users View)

• Accepts commands that make a Computer
  act/operate (Input, Store, Process, Output) all
  the time.
• Remove machine dependence for all possible
  applications as far as possible.
• Guarantees Response time for each user command.
• Provides a hospitable user friendly interface.

4
Role of any Operating System(System Designers
View)

• Shields ALL limitations of the underlying
  Architectural and / or System Software Support.
• 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
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).

9
File System

• Most visible aspect of any Operating System to
  the User ( Users interact most frequently).
• Provides the following facilities
• Mechanism for permanent / non volatile storage of
  information in various secondary medias.
• Presents an uniform logical view of all these
  storage medias to the user O.S.

10
File System (Key Features)

• Collection of Files stored on secondary medias.
  File A named collection of related
  information (Records) .
• A directory structure helps in the following
• - File Organization.
• - Access Rights (Protection
  Mechanism) .
• One or more Partitions ( Provides separation of
  directories useful for better manageability of
  large filing cabinet. )
• Implementation (Mapping from Logical viewpoint
  to Physical Media) .

11
Stored Information

• Programs
• User Programs Source, Object , Executable.
• System Programs Packages Executable.
• Data
• a) Text.
• b) Documents.
• c) Multi Media.

12
Type of a File (The type extension)

• File type associated with the file name itself
  in the following manner
• ltFile Name gt.ltExtension) File Type Specifier
  Stringgt
• ? Wild Card (ALL Types that share the same
  name)

13
File Types (Usage associated access)

• File Type used Extension Usage
  Accesibility
• --------------------------------------------------
  -------------
• Document doc, tex, pdf, ps Typed
  Documents Direct
• --------------------------------------------------
  ---------------------------------------
• Source c , c, asm , java
  Program Source Direct
• -------------------------------------------------
  ---------------------------------------
• archive arc, tar, zip
  Related files in Direct / Seq
• 
  Grouped , Compressed
• --------------------------------------------------
  ----------------------------------------
• Library lib , dll
  Support Routines Direct
• --------------------------------------------------
  ----------------------------------------
• Data Text txt, dat
  Textual Data Direct / Seq.
• --------------------------------------------------
  ------------------------------------------
• Multimedia mpeg, avi, jpeg Binary
  File containing Direct
• 
  Audio Video , Picture
• --------------------------------------------------
  -------------------------------------------
• Executable exe, com, bin
  Executable Module Direct / Seq.
• --------------------------------------------------
  --------------------------------------------
• Batch bat , sh
  Sequence of Commands Seq Preferable

14
Storage Medias (Filing Cabinets)

• Magnetic Tape Sequential Access.
• Disks
• 1. Magnetic Hard Disk (Direct Access
  Outer to Inner
• R/W Head floats inside an air
  cushion on the Disk surface).
• 2. Winchester Disk ( Hermitically
  Sealed Magnetic Hard
• Disk ).
• 3. Floppy Disk (Flexible magnetic
  Disk R/W Head
• comes into direct contact with
  Disk surface).
• 4. Optical Disks (CD_ROM,
  DVD_ROM,DVD_RAM,
• WORM ) Hard Disks, R/W Head
  LASER Beam ,
• Direct Access Inner to Outer.
• Pen Drive Electrically Alterable non Volatile
  Flash Memory.

15
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.

16
Directory Structure

• Linear ( Rarely Used).
• Hierarchical
• a) Tree / Acyclic Graph Mostly Used.
• b) Cyclic Graph Management difficult.

17
Hierarchical File Organization

• Tree Like Structure Directory is Head pointer
• 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

18
A typical File Descriptor

• Name/External Name A string of alphanumeric
  characters understood by the user (Human readable
  form).
• Identifier An unique tag, a number helps to
  identify the file in a file system used by the
  O.S. (non human accessible).
• Type Helps to identify the area of use of the
  file (To be illustrated later) (Human readable
  form).
• Size/Length in bytes /Blocks . Maximum allowed
  size is specified sometimes (Human readable
  form).
• Protection Accessibility Control Based on
  user Group (Partly Human readable form).
• Owner Identification Related to user id.
  (Human readable form).
• Time Date (Human readable form) constitutes
  of one or more of the following
• - File Creation Date Time.
• - Last modification Date Time.
• - Last access Date Time.
• Location Pointer to the start (sometimes also
  the Last) physical block of the file as stored on
  the secondary media (Non Human accessible but
  O.S. readable).
• State Open / Closed.
• Sharing Attribute
• Storage Device Details System accessibility.
• N.B
• Any Directory is also a File.
• Each File is also a structured Abstract Data
  Type (ADT).

19
Basic File Operations

• Creation of a new File CREATE FILE.
• Deletion of an Existing File DELETE FILE.
• Opening an Existing File OPEN FILE.
• All types of file element (Record) accesses
  (to be illustrated shortly) must be preceded by
  OPEN FILE. This is necessary for activating the
  file access mechanism.
• Closing an Opened File CLOSE FILE. (After all
  references / accesses to that file are finished).

20
File System Software Architecture

• User Program
• File Organization

Logical I/O
Basic I/O Supervisor
Basic File System
Device Interface
21
Informations associated with an Open File

• Access Rights Obtained from the directory
  matched with Access Requesting Process Id . Used
  to regulate the file accessibility from each of
  the requesting processes. Contained in the
  System File Table.
• Start Pointer Address of the starting block of
  the File on Secondary Media. Contained in the
  System File Table.
• Current File Position Pointer Unique to each
  Reader processes accessing the file contained in
  the Process File Table.. Assuming a single file
  writer process and no other access during
  writing.
• Open Count Non zero Integer counter indicating
  number of processes currently accessing the file.
  Contained in the Process File Table as well as a
  part of the System File Table. Each open call by
  a process of a particular file increments this
  counter.
• Current Access Date Directory entry used
  updated by the System File Table.
• File Size Directory entry used updated by the
  System File Table.

22
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.

23
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
24
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 .

25
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.

26
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).

27
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.

28
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.

29
State of the Art Operating Systems

• Category A
• Proprietary needs license WINDOWS by Microsoft
  , MAC from Apple, UNIX from Bell Labs .
• Open Source like LINUX.
• Category B
• Single User WINDOWS Desktop / Personal Edition
  , LINUX
• Multi User WINDOWS Server, LINUX Server,
  UNIX .
• Distributed LINUX, UNIX, WINDOWS with .NET
• Category C Multi User Category
• Multi_Processing.
• Multi Tasking.
• Multi Threading Hyper Threading.

30
More Facility More Support

• Not all operating systems can be installed on
  any Computer System.
• Each Operating System needs some specific
  Architectural Support in the form of
• a) Minimum CPU Speed Clock Frequency
• b) Minimum CPU Operand Size in bits.
• c) Minimum available Electronic Memory.
• d) Minimum available Secondary Memory / Disk
  Size.

31
The WINDOWS Hierarchy

• WINDOWS 3.1 8/ 16 Bit CPU, 128 MB RAM, 10 GB
  HDD
• WINDOWS 95 16 Bit CPU , 128/256 MB RAM. 10 GB
  HDD
• WINDOWS 98 32 bit CPU , 800 MHz CPU, 256 MB RAM
  recommended, 20/ 40 GB HDD
• WINDOWS 2000 32 bit CPU minimum 1.d GHZ, 256 MB
  RAM, 40 GB HDD
• WINDOWS 2003 Not Popular
• WINDOWS XP 32 Bit , 2 GHz above CPU , 512 MB
  RAM, 40 GB upwards HDD
• WINDOWS VISTA ( Proposed Name Long Horn) 32 bit
  , 2.6 GHz above CPU , 2 GB RAM, 80 GB upwards
  HDD

32
The Various LINUX Distributions

• Red Hat ( Various versions Editions )
• Debian. ( Various versions Editions )
• Fedora. ( Various versions Editions )
• Mandrake . ( Various versions Editions )
• Upgraded one will have a different Version Number
  as well as a slightly modified Core / Kernel.