BSC CSIT Semester 4 – Operating System () Questions & Answers | Past TU Exam Papers

Question 1

3) Suppose that the disk drive has 50 cylinders, numbered from 0 to 49. The drive is currently serving the request at cylinder 20 and the previous request was at cylinder 25. The queue of pe

Marks: 10

Year: 2070 Final TU

Disk Scheduling Algorithms and Seek Time Calculation Given: - Cylinders: 0–49 - Current head: 20 - Previous request: 25 → direction = toward lower cylinders - Request queue: 10, 22, 20, 2, 40,

Question 2

What is “device independence”? Define.

Marks: 5

Year: 2070 Final TU

Device Independence in Operating Systems Definition Device Independence is the property of an operating system that allows programs to access and use I/O devices without needing to know the details o

Question 3

Suppose the head of a moving- head disk with 200 tracks, numbered 0 to 199 is currently serving request at tracks 143 and has finished a request at track 125. The queue it requests is kept in the FIFO

Marks: 10

Year: 2071 Final TU

Disk Scheduling Algorithms and Total Head Movement Given: - Disk tracks: 0 – 199 - Current head: 143 - Previous head: 125 → direction = toward higher tracks - Request queue (FIFO): 86, 147, 91,

Question 4

What is DMA? Explain how it works.

Marks: 5

Year: 2071 Final TU

Direct Memory Access (DMA) 1. Definition - DMA (Direct Memory Access) is a method by which I/O devices can transfer data directly to or from main memory without involving the CPU for each byte/word t

Question 5

How does DMA increase system concurrency? How does it complicate hardware design?

Marks: 5

Year: 2072 Final TU

Direct Memory Access (DMA) and System Concurrency 1. Definition of DMA: - Direct Memory Access (DMA) is a technique that allows peripheral devices to transfer data directly to/from main memory without

Question 6

Write short notes on:\ (a) Disk formatting\ (b) Memory Mapped I/O

Marks: 5

Year: 2072 Final TU

Short Notes (a) Disk Formatting - Definition: Disk formatting is the process of preparing a storage device (hard disk, SSD, or floppy) to store data. - Purpose: 1. Creates a file system (e.g.,

Question 7

What is the main objective of disk scheduling algorithms? why SSTF is not practically feasible? Assume that we have disk with 100 tracks and currently head is at track number 35. What will be the seek

Marks: 10

Year: 2076 Final TU

(a) Main objective of disk scheduling algorithms The main objective is to minimize disk head movement (seek time) so as to: - Reduce average seek time and latency, - Improve throughput (I/O requests s

Question 8

When programmed IO is suitable than other IO handling techniques? Explain the process of IO handling using DMA.

Marks: 5

Year: 2076 Final TU

When Programmed I/O is More Suitable Programmed I/O (PIO) is suitable in situations where: - Low-speed I/O devices are used (e.g., keyboard, mouse, simple sensors). - Data transfer is small and infreq

Question 9

Why the concept of disk interleaving is important? Explain with suitable example.

Marks: 5

Year: 2078 Final TU

Disk Interleaving 1. Definition: - Disk interleaving is the technique of rearranging sectors on a disk so that consecutive sectors of a file are spaced apart physically to match the speed of the CPU o

Question 10

How DMA operation is performed? Consider a disk with 200 tracks and the queue has random requests from different processes in the order :\( 45, 48, 29, 17, 80, 150, 28\) and \(188\). Find the seek tim

Marks: 10

Year: 2080 Final TU

1. Direct Memory Access (DMA) Definition: - DMA is a method that allows I/O devices to transfer data directly to/from memory without CPU intervention. - CPU is only involved at the start and end o

Question 11

Find the seek time using SCAN, C-SCAN, Look and C-Look disk scheduling algorithms for processing the following request queue: \(35, 70, 45, 15, 65, 20, 80, 90, 75, 130.\) Suppose the disk has tracks n

Marks: 10

Year: 2081 Final TU

Disk Scheduling — SCAN, C-SCAN, LOOK and C-LOOK Given: - Disk tracks: 0 .. 150 - Initial head position = 30 - Head direction = outward (toward higher track numbers) - Request queue: 35, 70, 45,

Question 12

Explain memory-mapped I/O.

Marks: 5

Year: 2081 Final TU

Memory-Mapped I/O Definition: Memory-Mapped I/O (MMIO) is a technique where I/O devices are treated as if they are memory locations. The CPU can read from or write to these device registers using st

Question 13

Define shell and system call. suppose a disk has 201 cylinders, numbered from 0 to 200. At same time the disk arm is at cylinder 95, and there is a queue of disk access requests for cylinders 82,170,4

Marks: 10

Year: 2079 Final TU

1. Definitions Shell - A shell is an interface between the user and the operating system. - It allows users to execute commands, run programs, and interact with the kernel. - Example: Bash, Zsh,

Question 14

Describe the working mechanism of DMA.

Marks: 5

Year: 2079 Final TU

Direct Memory Access (DMA) Definition: DMA is a method by which an I/O device can transfer data directly to/from memory without continuous CPU intervention. It improves system efficiency by allowing

Question 15

What is the task of disk controller ? List some drawback of segmentation.

Marks: 5

Year: 2079 Final TU

1. Task of Disk Controller A disk controller is a hardware component that manages the communication between the CPU and disk drives. Its main tasks are: 1. Data Transfer Management: - Controls re

Question 16

Suppose a disk has 201 cylinders, numbered from 0 to 200. At same time the disk arm is at cylinder 10, and there is a queue of disk access requests for cylinders \(30, 85, 90, 100, 105, 110, 135,\) an

Marks: 5

Year: 2080 Final TU

Disk Scheduling Example Given: - Disk cylinders = 0 to 200 - Current head position = 10 - Request queue: 30, 85, 90, 100, 105, 110, 135, 145 - Head moving inward (toward lower cylinder numbers)

Question 17

What are the advantages of using interrupt? Describe.

Marks: 5

Year: 2080 Final TU

Advantages of Using Interrupts Definition: - An interrupt is a signal sent to the CPU by hardware or software indicating an event that needs immediate attention. - It temporarily halts the CPU’s c