• CPU Scheduling
• Page Replacement in OS
• Disk Scheduling
• OS - Introduction
• OS - Processes
• Memory Management
• Input Output
• File Management
• FAQs - I
• FAQs - II
• FAQ - III

Operating System

FAQ - III

1. What is Device Management?

   Answer: Device management is the function of an operating system responsible for managing hardware I/O devices such as:

   • Keyboard
   • Mouse
   • Printer
   • Disk
   • Network Devices
   • Display
   The OS uses device drivers and I/O-management techniques to control these devices. Major functions of Device management are:
   • Device allocation
   • Device scheduling
   • Device-driver management
   • Buffering
   • Error handling
   • I/O coordination

2. Explain Polling in an I/O System.

   Answer: Polling is an I/O technique in which the CPU repeatedly checks a device to determine whether it requires service. The CPU continues checking until the device becomes ready. Polling can waste CPU time because the CPU repeatedly checks the device even when no I/O event has occurred.

3. Compare Interrupt-Drive I/O with Polling.

   Answer:

   Polling	Interrupt-Driven I/O
   CPU repeatedly checks device status	Device sends an interrupt when service is needed
   CPU may waste time checking	CPU can perform other work
   Simple to implement	More complex
   Suitable in some simple systems	Generally more efficient for asynchronous events

4. Define Direct Memory Access (DMA).

   Answer: Direct Memory Access (DMA) is a technique that allows an I/O device to transfer data directly to or from main memory without requiring the CPU to handle every individual byte or word.

   CPU --> DMA Controller --> Device, Main Memory
   The CPU typically initializes the DMA transfer, and the DMA controller performs the data transfer. After completion, the controller can interrupt the CPU. DMA significantly reduces CPU overhead during large data transfers.
5. How Does Multithreading Perform Better Than Single Threading?

   Answer: Multithreading can improve performance because multiple threads can execute different parts of a program concurrently. Advantages include:

   • Responsiveness: One thread can continue while another waits.
   • Resource sharing: Threads share the same process resources.
   • Economy: Creating threads is generally cheaper than creating processes.
   • Parallelism: On multicore processors, multiple threads can execute simultaneously.
   • Better CPU utilization: CPU time can be used while another thread waits for I/O.
   Example:
   

   Single Thread: CPU --> Computation --> I/O wait -- > Computation

   Multiple Threads:

6. Thread 1 --> Computation --> I/O wait
7. Thread 2 --> Computation --> Computation
8. Thread 3 --> I/O --> Computation
Thus, multithreading can improve responsiveness and CPU utilization.
9. Compare Authentication with Authorization.

   Answer:

   Authentication	Authorization
   Verifies who the user is	Determines what the user is allowed to do
   Happens before authorization	Usually occurs after authentication
   Example: username/password	Example: permission to delete a product
   Answers: Who are you?	Answers: What can you do?

   Authentication mechanisms

   • Username and password
   • PIN
   • OTP
   • Biometrics
   • Security tokens
   • Multi-factor authentication
   • Digital certificates

   Authorization mechanisms

   • Role-Based Access Control (RBAC)
   • Attribute-Based Access Control (ABAC)
   • Access Control Lists (ACL)
   • Capability-based access control
   • Permission-based access control