This Tutorial will provide you information on working of operating system. Main topics are following and further sub-topics are discussed in detail. 1. Kernel Architecture. 2. Initialization of operating system. 3. Process of operating system. 4. Management in operating system. 5. File system. 6.Security in operating system. 7.Interface in operating System.

1. OPERATING SYSTEM
FAHAD FAROOQ

2. CONTENTS:
 Kernel architecture
 Initialization
 Process
 Management
 File system
 Security
 Interface

3. OPERATING SYSTEM
• OS is a system software that runs the hardware.
• It enables the application to interact with hardware.
• It handles input output ,control peripheral devices, manage processes and
communicates with resources.
• Found on cellular phones, web servers, automobile,
video game consoles and PCs.
• Windows OS, Embedded OS, Unix OS ,Linux OS

4. Functions of OS:
Operati
ng
system
Process
manage
ment
Interrup
ts
Memory
manage
ments
Device
drivers
networki
ng
security
I/o
File
system

5. Kernel:
• Kernel is a central module of operating system.
• It is the first program loaded on start up and remains in main memory.
• Kernel connects application software to hardware and provide
services.
• Typically responsible for Memory Management, Device Management
and System Calls.
• Monolithic kernels, Exokernels, Micro kernels,
Hybrid kernels etc.

6. Types of kernels:
Typically based on the security level or abstraction level.
•Monolithic Kernel:
 Entire operating system works in
Kernel Space.
 It is fast but larger than other kernels
and difficult to debug.
 Linux, Unix , DOS, Windows 95 and
many more.
•Micro Kernel:
 Small in size divided the servers in
kernel space and user space.
 Slower than Monolithic kernel but easy
to debug and secure.
 Symbian, iOS, MINIX 3, XNu

7. Monolithic Kernel and Microkernel:

8. Hybrid kernel:
• Combination of Monolithic kernel and Micro kernel Architecture.
• Both technology architectures are used to take benefits.
• Two layers are being setup user space and kernel space.
• Windows NT, Windows Server 2012, Xbox one, Windows phone 8

9. Comparison of kernels:

10. Processes in operating system:

11. Initialization:
• Initialization is the process of how the computer boots and loads.
• Computer initialization runs a series of tests to verify efficiency and load
drivers for the system
• Two processes discussed
• Bootloader
• Hardware Initialization

12. Interrupts:
• Interrupt is a signal to the processor emitted by hardware or software
indicating an event that needs immediate attention
• The interrupt handler prioritizes the interrupts
• Interrupts give the user better control over the computer.
• 2 types of interrupts
• Hardware Interrupts are generated by hardware
devices
• A software interrupt is caused by an exceptional
condition in the processor

13. Context switching:
• Switching of the CPU from one process or thread to another.
• Also called “process switch or a task switch”
• Essential feature of multitasking operating systems
• Requires considerable processor time

14. Scheduling:
• Act of determining which process in the ready state should be moved to
the running state
• The prime aim of the process scheduling system is to deliver minimum
response time for all programs & make the system efficient, fast and fair.
• Scheduling allows multiple users to share system resources effectively
• Scheduler figures out which program to give control to next.

15. Difference between preemptive and non
preemptive scheduling:
•Preemptive
• The process with the highest
priority should always be the one
currently using the resources.
• Resources are only allocated for a
limited time and the process can be
interrupted in between
• Scheduling which takes place when
a process switches from running
state to ready state or vice versa
•Non-preemptive
• A process runs to completion when
scheduled
• Once resources are allocated to a
process, the process holds it till it
completes its time
• The scheduling which takes place
when a process terminates or
switches from running to waiting
state

16. Concurrent processes:
• Computing model in which multiple processes executing during the same
period of time
•Advantages:
• Increased program throughput
• High responsiveness for input/output
• More appropriate program structure

17. Inter process communication (IPC):
• Mechanism that allows the exchange of data between processes
•Advantages:
• Helps a programmer organize the activities among different
processes.
• Allows one application to control another application, thereby
enabling data sharing without interference.
• Facilitates efficient message transfer between processes
• Enables data communication by allowing to share memory and
information

18. IPC Mechanism:

19. Hardware initialization:
• All processor based boards need testing to confirm the correctness of
hardware design and proper functioning of various peripherals
• It is a process used to check the proper functioning of all the hardware
components in a system.

20. Bootloader (boot process/bootstrap):
• Bootloader is a piece of code that runs before any operating system is
running.
• It is loaded by the computer's BIOS ROM
• It is highly processor and board specific.
• The bootloader performs the necessary initializations to prepare the system
for the operating system.
• It tells the computer what to do after the system is turned on.

21. Scheduling criteria:
• CPU utilization
• Throughput
• Turnaround time
• Waiting time
• Load average
• Response time

22. Scheduling:
•First come first served
• Jobs are executed on first come, first serve basis.
• Easy to understand and implement
• Poor in performance as average wait time is high.
• Shortest remaining time
• Selects the process for execution which has the
smallest amount of time remaining until completion .
• It mostly gives minimum average waiting time.

23. Scheduling:
•Round Robin Scheduling
• Very common base policy.
• Run each process for its time duration (scheduling
quantum)
• After each time slice (duration), moves the running
process to the back of the queue.
• Priority Scheduling
• Priority scheduling is a method of scheduling processes
based on priority
• Processes with higher priorities are carried out first
• Priority can be decided based on memory requirements,
time requirements or any other resource requirement.

24. Scheduling:
•Shortest job next
• Also known as shortest process next, shortest job first, or
SJF
• Best approach to minimize waiting time.
• The shortest job is executed first
• Preemptive SJF is called SRTF - shortest remaining time
first.

25. Deadlock:
• Deadlocks are a set of blocked processes each holding a resource and
waiting to acquire a resource held by another process.
• Deadlock occurs if any one of the condition is true
• Mutual exclusion condition
• Hold and wait condition
• No preemption condition
• Circular wait condition
• Deadlock causes a process to freeze.
• Deadlock causes starvation

26. Starvation and livelock:
•Starvation:
• A process is in starvation when it is waiting for a resource that
is continuously given to other processes.
• The entire system of processes hasn't come to halt in
starvation
•Livelock:
• situation in which two or more processes continuously change
their state in response to changes in the other process(es)
without doing any useful work.
• Neither process is blocked or waiting for resources in case of a
livelock

27. Deadlock:

28. Deadlock:

29. Locks & signals:
•Locks:
• used to prevent multiple threads from accessing a resource at
the same time
•Signals:
• The mechanism whereby processes are made aware of events
occurring
• Sent to the current process telling it what it needs to do

30. Semaphores:
• Non negative integer variable used to do the following tasks
• check the availability of resources for a task
• control access to a common resource by
multiple processes
• A system to ensure process cannot enter critical
region if another process is in it’s
• 2 types
• Binary semaphore(value either 0 or 1)
• Counting semaphore(value greater than 1)

31. Semaphore:

32. Pre emptive & round robin scheduling:
Pre-emptive
scheduling
Round Robin
scheduling

33. IPC:

34. What does mutual exclusion (mutex) mean?
• A mutual exclusion (mutex) is a program object that prevents
simultaneous access to a shared resource
• . This concept is used in concurrent programming with a critical section,
a piece of code in which processes or threads access a shared resource
• . Only one thread owns the mutex at a time, thus a mutex with a unique
name is created when a program starts

35. Physical memory:
• Physical memory refers to the actual RAM of the system,.
• Also called primary memory.
• it is the only storage type directly accessibly to the CPU.
• Holds the instructions of programs to execute.

36. Segmentation:
• A segment has a set of permissions, and a length, associated with it.
• It may also have a flag indicating whether the segment is present in
main memory or not; if the segment is not present in main memory,
an exception is raised, and the operating system will read the
segment into memory from secondary storage
• A memory management unit (MMU) is responsible for translating a
segment

37. Virtual memory:
• Virtual memory is a memory management technique that offers two
main benefits:
• Each process "thinks" it has all the system's memory to itself
• It becomes possible to access more memory than the actual physical
amount
• Virtual memory is very useful and is implemented in most operating
systems by using the memory management unit (MMU) in the CPU.

38. Paging:
• In computer operating systems there are various ways in which the
operating system can store and retrieve data from secondary storage for
use in main memory.
• One such memory management scheme is referred to as paging.
• In the paging memory-management scheme, the operating system
retrieves data from secondary storage in same-size blocks called pages.

39. Swapping:
• Swapping concept comes in terms of process scheduling.
• Medium term scheduler removes process from CPU for duration and reduce the
degree of multiprogramming.
• After some time these process can again be reintroduced into main memory.
• Process execution will again be resumed from the point it left CPU.
• This scheme is called swapping.
• More generally we can say swapping is removing of process from memory to
secondary memory and again back to main memory.

40. • Memory management handles primary memory and moves processes
back and forth between main memory and disk during execution.
• Memory management keeps track of each and every memory location.
• It checks how much memory is to be allocated to processes.
• It decides which process will get memory at what time.
• It tracks whenever some memory gets freed or unallocated and
correspondingly it updates the status.
Memory management:

41. Fault tolerance:
• Fault tolerance is the property that enables a system to continue
operating properly in the event of the failure of (or one or more faults
within) some of its components.
• If its operating quality decreases at all, the decrease is proportional to
the severity of the failure, as compared to a naively designed system in
which even a small failure can cause total breakdown.

42. File system, Abstraction:
• A file system is a way of organizing information on a physical drive or other
media (e.g. RAM) for access. In general, file systems can be divided into several
groups:
• With a filesystem, we can organize our data into files, directories, and other
constructs, and manipulate them in various ways.
• To open a file, you need only its path; it's not necessary to figure out the exact
location on disk and instruct the hard drive controller to move the read head to
that position.

43. Allocation algorithm:
• Effective utilization of file space and fast access of the files.
There are three types of allocation:
1.contiguous allocation
2.linked allocation
3.indexed allocation
• In addition to storing the actual file data on the disk drive, the file system
also stores metadata about the files: the name of each file, when it was last
edited, exactly where it is on the disk, and what parts of the disk are "free".
Free areas are not currently in use by the file data or the metadata, and so
available for storing new files. (The places where this metadata is stored are
often called "inodes", "chunks", "file allocation tables", etc.)

44. Fault tolerance:
• fault-tolerance refers to the ability of something to continue to function
(though perhaps at reduced levels) after something as gone wrong.
• Many things can go wrong in a storage system, especially one with
moving parts like hard disk drives.
• Bad sectors only prevent the use of a few sectors, while a head crash can
permanently ruin an entire disk.

45. Raid:
• RAID (Redundant Array of Independent Disks) is a method of storing
data combines multiple physical drives into one unit.
• Data is distributed and duplicated across the drives in various ways.
• The term has now come to mean any technology that divides and
replicates data over multiple drives.

46. Journaling:
• Journaling is a technique for fault tolerance in file systems.
• It works by keeping track of all changes in a log (a "journal") before
committing the changes themselves to disk.
• This makes crashes and power failures easier to recover from and less
likely to cause permanent data loss or space leakage.

47. Bad blocks:
• which prevents use of corrupted disk sectors.

48. New technology file system, ext4:
• NTFS is a file system by Microsoft. This is default file system of Windows NT,
Windows Server, Windows XP, and Windows Vista, Windows 7.
• There are open-source applications that are able to reliably read/write to it.
• ext4 is the open source file system used on many Linux distributions,
including Android 2.3 and later. It is a journaled file system, like its
predecessor ext3.

49. Other’s file system:
• Operating systems tend to recommend using
(and so support natively) file systems
specifically designed for them; for example,
NTFS in Windows and ext3 and ReiserFS in
Linux. However, in practice, third party drivers
are usually available to give support for the
most widely used file systems in most general-
purpose operating systems (for example, NTFS
is available in Linux through NTFS-3g, and
ext2/3 and ReiserFS are available in Windows
through third-party software).

50. Security:
• It is the process of ensuring OS
Integrity, confidentiality and
availability.
• OS security refers to specified
steps or measures used to protect
the OS from threats, viruses,
worms, malware or remote hacker
intrusions

51. Typical security attack:

52. User interface (UI):
• The means by which the user and a computer system interact, in particular the
use of input devices and software.
• System users often judge a system by its interface rather than its functionality.
• Poor user interface design is the reason why so many software systems are
never used
• Types : 1. CLI 2. GUI

53. CLI:
a. User types commands to instruct
system e.g. Unix
b. May be implemented using cheap
terminals.
c. Easy to process using compiler
techniques
d. Commands of arbitrary complexity can
be created by command combination.
GUI :
a. Fast, full-screen interaction
b. The user may switch quickly from one
task to another
c. Interact with several different
applications.

54. CLI & GUI Example:

55. Multiple user interface:

56. THANK YOU !