Operating system

1. I/O Devices Protection
Internal topic
Presented by Muhammad Abdullah
Roll no. BSF2103722
Topic
no.1

2. Introduction:
 I/O protection in operating systems is an essential mechanism to provide
secure access to I/O devices from user and kernel modes
 In most operating systems, I/O protection is implemented using the concept
of I/O privilege levels or rings. The processor and the operating system define
four different privilege levels, also called rings, where ring 0 is the highest
and contains the kernel mode, while ring 3 is the lowest and contains the user
mode.

3. I/O Protection Issued:
 An I/O instruction issued by a process in user mode has to be executed with a
privileged instruction in the kernel mode. The kernel mode is the only ring
that can directly access the hardware. The operating system sets up I/O
privilege levels to control access to I/O devices by processes running at
different privilege levels.

4. Importance:
 The protection is provided through hardware-based features like device
controllers, memory-mapped I/O, and system calls, used in the operating
system to provide access to I/O devices.
 In I/O protection, every I/O device is allocated a unique I/O space or I/O
ports that are accessible only by the kernels to avoid unauthorized access.
The operating system maintains a mapping between the device drivers and
memory buffers, and the device controllers are programmed to treat all I/O
addresses generated by user processes as invalid.
 The operating system also provides mechanisms such as input and output
permission bits that restrict the access to I/O devices for all the user
processes. The permission bits help ensure that no unauthorized process can
gain access to the device.
 The I/O protection in modern operating systems also incorporates Virtual
Memory Management (VMM) technology with page-level protection. With this
technology, the kernel provides a different map of the physical memory in
each process's virtual address space, and every process can access a unique
copy of the data.

5. Function:
 The primary function of I/O protection in operating systems is to provide a
secure layer of access control to Input/output (I/O) devices, ensuring that
only authorized processes and users can access I/O devices. Here are some of
the main functions of I/O protection:

6. 1. Prevent unauthorized access:
 I/O protection mechanisms ensure that only authenticated and authorized
processes can interact with I/O devices. Unauthorized access can lead to data
theft, data loss, or other security breaches

7. 2. Maintain data integrity:
 I/O protection ensures that data being read from or written to I/O devices is
protected from unauthorized access, unauthorized modification or deletion,
and corruption.

8. 3. Provide isolation:
 By implementing I/O protection, processes are prevented from accessing
other processes' I/O data, enhancing security and preventing critical data
breaches.

9. 4. Prevent system crashes:
 The proper protection of I/O devices prevents device drivers from accessing
memory outside their allocated memory space, thereby preventing system
crashes.

10. 5. Support multi-user environment:
 I/O protection plays a crucial role in supporting a multi-user operating
system environment by ensuring that each user can only access and
communicate with the devices authorized for their account

11. 6. Support virtual machines:
 In virtual machine environments, I/O protection mechanisms ensure that
virtual machine guests cannot access I/O devices other than those allowed by
their virtual machine host.

12. Summary:
 In summary, I/O protection mechanisms are essential in operating systems to
control access to I/O devices and to prevent unauthorized access, thereby
ensuring the security of the system.

13. Process Synchronization
External topic
Presented by Muhammad Abdullah
Roll no. Bsf2103722
Topic
no.2

14. Introduction
 Synchronization refers to the coordination of activities or processes to ensure
that they happen in the correct order and at the right time. In computing,
synchronization is particularly important when multiple processes or threads
are accessing shared resources, as it ensures that all processes have access to
the resource at the correct time and in the correct order.
 In an operating system, process synchronization refers to the techniques and
mechanisms used to ensure that multiple processes or threads do not
interfere with each other and that they access shared resources in a
coordinated and controlled manner. Some common examples of shared
resources include memory, files, and hardware devices.

15. Example:
 Where two processes try to update the same variable in memory. If both
processes attempt to update the variable at the same time, its values can
become inconsistent or corrupt. To avoid this, synchronization mechanisms
can be used to enforce mutual exclusion and ensure that only one process can
update the variable at a time. One way to achieve this is using a mutex. In
this case, the variable and a corresponding mutex are shared between the
two processes. Before accessing the variable, each process checks if the
mutex is locked by another process, and if it is, it waits until the mutex is
released. Once the mutex is released, the process can acquire it, update the
variable, and release the mutex to allow other processes to access it.

16. Example:
 Here's an example in pseudocode:
Process 1:
acquire(mutex)
variable = variable + 1
release(mutex)
Process 2:
acquire(mutex)
variable = variable – 1
release(mutex)
In this example, each process acquires the mutex and updates the variable inside a critical
section. The mutex ensures that only one process can update the variable at a time,
preventing any race conditions or inconsistencies. This is just one example of how
synchronization can be used to ensure correct and efficient execution of processes in an
operating system. Other synchronization mechanisms like semaphores, monitors, and
barriers can also be used to manage access to shared resources and prevent conflicts
between processes

17. There are several common techniques for
achieving synchronization in computer
systems. These include

18. 1. locking:
 A lock is a synchronization mechanism that ensures that only one process or
thread can access a shared resource at a time. Locking is typically
implemented using mutexes or semaphores to ensure that the resource is
properly protected
2. Atomic operations:
 An atomic operation is an operation that is indivisible and uninterruptible.
Atomic operations are typically used to ensure that multiple processes do not
interfere with each other when accessing the same memory location.

19. 3. Barrier synchronization:
 A barrier is a synchronization mechanism that ensures that all processes or
threads have reached a certain point in their execution before continuing.
Barriers are commonly used in parallel processing to ensure that all processes
have completed their work before continuing to the next phase of processing
4. Message passing:
 Message passing is a communication mechanism where processes or threads
send messages to each other to coordinate their activities. This mechanism is
commonly used in distributed systems to ensure that all processes are aware
of each other's activities and progress.

20. 5. Semaphores:
 A semaphore is a data structure that is used to control access to shared
resources. It can be used to ensure that only one process or thread can access
a shared resource at any given time. Semaphores can be either binary or
counting, and they can be used to enforce mutual exclusion, synchronization,
and resource allocation.
6. Mutexes:
 A mutex is a programming object used to protect shared resources by creating
a critical section. Only one thread can access the shared resource when the
mutex is locked. If another thread tries to access the same resource while it
is locked, it will wait until the mutex is released

21. 7. Monitors:
 A monitor is a higher-level abstraction of a mutex. A monitor provides a
mechanism for multiple threads to access shared resources in a synchronized
way. Programmers use monitors to specify which code is a critical section or a
region that requires exclusive access to shared resources

22. Function of Synchronization
Here are some specific functions of synchronization in an operating system:
1. Mutual Exclusion: With mutual exclusion, only one process or thread can access a
shared resource at any given time, ensuring data consistency and preventing conflicts
that may arise when multiple processes are trying to access the same resource
simultaneously.
2. 2. Coordination: Coordination mechanisms are used to ensure the correct order of
execution of operations involving shared resources among concurrent processes. For
example, a synchronization mechanism can be used to ensure that a dependent process
waits until a required resource is available and can access it.
3. : Deadlocks can occur when multiple processes are waiting to acquire resources that
are locked by other processes. Using synchronization mechanisms such as timeouts or
prioritization can help prevent deadlocks by ensuring that resources are released or
given higher priority to certain processes

23. Summary
 Overall, synchronization is a vital aspect of computer systems, particularly in
multi-process or multi-threaded environments where shared resources are
common. By using synchronization mechanisms like locking and barrier
synchronization, systems can ensure that all processes and threads operate
correctly and in the appropriate order

24. MCQS
1. Which of the following is a technique used for thread communication?
A. Pipes
B. Signals
C. Shared memory
D. All of the above.
2. What is the difference between synchronization and concurrency?
A. Synchronization refers to the process of coordinating access to shared resources,
while concurrency refers to the ability of multiple tasks to execute at the same
time.
B. Synchronization refers to the ability of multiple tasks to execute at the same
time, while concurrency refers to the process of coordinating access to shared
resources.
C. Synchronization and concurrency are the same thing.
D. None of the above.
3. Which of the following is a technique used to prevent deadlocks?
A. Resource allocation graphs
B. Banker's algorithm
C. Timeouts
D. All of the above

25. MCQS
4. What is a deadlock?
A. A situation where two or more threads are waiting indefinitely for a resource to
become available.
B. A situation where two or more threads access a shared resource and try to
change its value at the same time.
C. A situation where two or more threads are competing for the same resource.
D. A situation where two or more threads are executing in parallel
5. Which of the following is true about monitors?
A. Monitors are a synchronization mechanism used for thread communication and
synchronization.
B. Monitors use signals and wait queues to coordinate access to shared resources.
C. Monitors are implemented as a class with methods that are synchronized.
D. All of the above.
6. What is a mutex?
A. A type of lock that allows multiple threads to access a shared resource
simultaneously.
B. A synchronization mechanism that prevents deadlocks.
C. A data structure used for parallel processing.
D. A variable used for inter-process communication

26. MCQS
7. What is a semaphore?
A. A type of lock that allows multiple threads to access a shared resource
simultaneously.
B. A variable used for inter-process communication.
C. A synchronization mechanism that prevents deadlocks.
D. A data structure used for parallel processing.
8. What is a race condition?
A. A situation where two or more threads access a shared resource and try to
change its value at the same time.
B. A situation where two or more threads are waiting indefinitely for a resource to
become available.
C. A situation where two or more threads are competing for the same resource.
D. A situation where two or more threads are executing in parallel
9. Which of the following is NOT an example of synchronization in computer
science?
A. Locks
B. Semaphores
C. Interrupts
D. Monitors

27. What is synchronization in computer science?
A. The process of maintaining consistency and order between two or more
processes.
B. The process of managing multiple tasks on a single processor.
C. The process of preventing deadlocks in a system.
D. The process of parallel processing.
Short question
1. What is synchronization?
2. Write the function of synchronization?
3. What is mutexes?
4. What is semaphores?
5. How synchronization work ?
Long question
Write the technique to achieve the synchronization?

28. THANK YOU