1. OPERATING SYSTEM
Chapter-4

3. LETS EXPLORE OS
 Interface between user and the hardware
 Allocates and manages the resources-value
for money
 Reclaim lost resources
 Manages the input, processing and output eg.
Steward in a restaurant
 Transforms a raw piece of hardware into a
machine
 Supports all application software
 Loads programs into main memory

4. ABSTRACT VIEW OF SYSTEM
COMPONENTS

5. WHAT AN OS DOES FOR A
LIVING..
loop forever {
run the process for a while.
stop process and save its state.
load state of another process.
}

6. PROGRAM STATES

8. DIFFERENCE BETWEEN TYPES
OF PROGRAMS
 Do lot of
computation
 Eg. Programs
computing value of
π
 No wastage of CPU
time
 Do lot of I/O
transactions
 Eg. Online railway
reservation program
 Lot of CPU time is
wasted
COMPUTE BOUNDPROGRAMS I/OBOUNDPROGRAMS

9. MULTIPROGRAMMING
 Concurrent residency of many programs in the
main memory of the computer
 Reduced CPU idle time-GREATER CPU
EFFICIENCY
 Greater memory efficiency-COMPLETE
MEMORY UTILIZATION
 Eg. of multiprogramming OS are VAX, VMS,
UNIX

10. WORKING OF OS

12. FUNCTIONAL UNITS OF AN
OS

13. FUNCTIONAL UNITS OF AN
OS
 Schedular & resource allocator- decides when
to introduce new programs in memory and the
order of execution
 File manager-manages secondary or magnetic
storage, organizing and accessing data

14. FUNCTIONAL UNITS OF AN
OS
 I/O handler-manages I/O devices, handles
device errors, device independence, efficient
organization and access of data on I/O
devices
 Memory management-implements
multiprogramming, protection of user work
area, provides memory space to users
 Dispatcher-allocates CPU to next scheduled
program

15. AN OS IS A RESOURCE
ALLOCATOR
“Mama says: It’s good to share!”
 Multiple users (?) get all computing resources
“simultaneously”:
 Cpu time
 Memory (ram, swap, working set, virtual,..)
 File system (storage space)
 I/O devices (display, printers, mouse,..)
 Clock
 The OS should give every user the illusion that she
is getting all resources to herself (not sharing!)

17. PROCESSOR MANAGEMENT
 Time sharing scheduling (round robin)-
• Each program has a fixed amount of time to
execute
• After leaving CPU, current program joins at the
end of the queue
• Multiple users share the computer simultaneously
• Gives a feel of dedicated single user system
• Improved response time
• Provides interactive environment
• Resources can be shared

18. MEMORY MANAGEMENT
 Partitioning –
• To accommodate many programs in memory,
partitioning is done
• Can be fixed size partitions- equal / unequal
• Leads to memory wastage
OS
10K
10K
10K
OS
4K
6K
20K
EQUAL SIZED
PARTITIONS
UNEQUAL SIZED
PARTITIONS

20. MEMORY MANAGEMENT
Dynamic Memory Relocation-solution to memory
wastage

21. MEMORY MANAGEMENT
 Dynamic memory relocation
OS
10K-BLANK
6K-PROG B
4K-BLANK
8K-PROG D
2K-BLANK
OS
6K-PROG B
8K-PROG D
16K-BLANK
BEFORE
Memory wastage
AFTER DYNAMIC
RELOCATION

22. VIRTUAL MEMORY
• Allows writing programs larger than the main
memory
• Gives illusion of very large memory(combo of
auxiliary and main memory)
• Generates a virtual address-that is not a real
physical memory address
• Virtual address can be more than physical
address
• It is the logical / symbolic representation of a
location in hardware

23. VIRTUAL MEMORY
• OS divides main memory into equal size pages
• Pages and blocks are of same size
• Page is loaded in memory only on demand
• A page table helps keeping track of which page in
memory is storing which block
• Set of pages in main memory is known as
working set.

25. ADVANTAGES OF VIRTUAL
MEMORY
• Memory efficiency
• Only active pages(on demand) are resident in
the memory
• Any page of any program can fir into any page
of the main memory
• Protection
• There is separate page table for each user
• Sharing
• Same page can be shared by two programs
using the page table settings

26. DEVICE MANAGEMENT
 OS maintains speed balance between CPU and
I/O device
 Characteristics of I/O devices-
 Speed
 Unit of transfer
 Data representation
 Permissible operations
 Error conditions
 Sharing

27. BUFFERING
 A temporary storage area (buffers) to read data
from input device or send data to the output
device
 Keeps CPU busy
• Because I /O operation is slow

28. BUFFERING
• Input Buffering
• When two buffers are used it is known as Double Buffering

29. BUFFERING
• Output Buffering

30. SPOOLING
• Simultaneous Peripheral Operation on Line
• Helps buffering process
• Used for non-shareable devices
• Eg. Rush hour on printer
• Process held up--long waiting time
• In spooling data of every user is temporarily
written on hard disk

31. SPOOLING
• No held up processes
• Spooler pick data one by one from hard disk
• Sends in sequence to the printer
• Hard disk becomes virtual printer

33. FILE MANAGEMENT
 File organization techniques
• Sequential-in predefined order
• Direct- direct transfer b/w applications without
using OS
• Indexed sequential-data is indexed for fast
retrieval
•Relative - Records of the file are stored one after
another both physically and logically. Record with
sequence number 16 is located just after the 15th
record

34. FILE MANAGEMENT
 File management functions
• Create file
• Delete file
• Open an existing file-read only
• Open an existing file-read / write
• Rewind operation-tape files
• Security at three levels-DAR
• Do anything
• Append only
• Write only

35. TYPES OF OS

36. TIME SHARING SYSTEM
• Multiprogramming, multiuser & interactive OS
• Resources of a centralized system are shared
• Uses round robin scheduling
• Less response time
• Each user gets a feel of a dedicated system
• Only a portion of job resides in main memory,
rest on hard disk

38. DISTRIBUTED SYSTEMS
 Distribute the computation among several physical
processors.
 Lo o se ly co uple d syste m – each processor has its own
local memory; processors communicate with one
another through various communications lines, such as
high-speed buses or telephone lines.
 Advantages of distributed systems.
 Resources Sharing
 Computation speed up – load sharing
 Reliability
 Communications

39. DISTRIBUTED SYSTEMS
(CONT)
 Requires networking infrastructure.
 Local area networks (LAN) or Wide area
networks (WAN)
 May be either client-server or peer-to-peer
systems.

41. REAL-TIME SYSTEMS
 Often used as a control device in a
dedicated application such as
controlling scientific experiments,
medical imaging systems, industrial
control systems, and some display
systems.
 Well-defined fixed-time constraints.
 Real-Time systems may be either hard
or so ft real-time.

42. REAL-TIME SYSTEMS
(CONT.)
 Hard real-time:
 Secondary storage limited or absent, data
stored in short term memory, or read-only
memory (ROM)
 Conflicts with time-sharing systems, not
supported by general-purpose operating
systems.
 Soft real-time
 Limited utility in industrial control of robotics
 Useful in applications (multimedia, virtual
reality) requiring advanced operating-system

43. MULTITASKING
 To handle two or more programs at the same
time from a single user’s perception
 CPU can perform only one task at a time,
however it runs so fast that it seems 2 or more
jobs seem to execute at the same time

44. BATCH PROCESSING
SYSTEM

46. JOB DESCRIPTION IN JCL

48. MULTIPROCESSING SYSTEM-
TYPES

49. MULTIPROCESSING SYSTEM-
TYPES
 Tightly coupled
• Processors share memory and I/O systems
• Shared memory access
• Smoothens information interchange
• Good synchronization among processes

51. FLYNN’S CLASSIFICATION OF
COMPUTERS

52. FLYNN’S CLASSIFICATION OF
COMPUTERS
 SIMD-Single instruction multiple data
• Array of n number of processing elements
• Identical elements controlled by master
controller
• Single instruction operates on multiple data
• Eg. Connection machine uses SIMD
architecture

54. SIMD VERSUS MIMD
Practical Differences
SIMD and MIMD are different in practice. SIMD is often used for
problems requiring lots of computations with processors performing
the same operation in parallel. MIMD is often used for problems
requiring algorithms broken up into parts that are separate and
independent, with each part being assigned to a different processor for
simultaneous solution.
Technical Differences
SIMD and MIMD are also technically different. SIMD processors tend
to be simpler, smaller, cheaper and faster than MIMD processors, but
MIMD is capable of more complex operations. MIMD operations that
the SIMD architecture can accomplish tend to take more time with
SIMD than with using the MIMD architecture. SIMD processors must
perform complex operations sequentially, while MIMD processors can
do this concurrently.

56. MULTIPROCESSING
CONFIGURATIONS
 Separate supervisor configuration
• Each processor has individual copy of OS
input, output and file system.
• Limited parallel processing is possible
 Master slave configuration
• A master processor controls all processors
and assigns work to them.
• Parallel processing possible

57. MULTIPROCESSING
CONFIGURATIONS
 Symmetric configuration
• Also known as Floating Master
configuration
• All processors are equal and independent
• Only one processor executes the OS at a
time
• Parallel processing allowed

59. GUI INTERFACE
 Uses computer graphics to make program
easier to use
 Contains icons for navigation
 Selection done by mouse instead of
commands through keyboard

60. DIFFERENT TYPES OF OS

62. OBJECT LINKING &
EMBEDDING