1What is the lowest level of a file system?
Secondary storage
2What is the progression of storage devices from older to newer technology?
From magnetic tapes to disks
3Why are magnetic tapes still used today?
They are primarily used for storage and backup of infrequently used data due to their slow access times
4How is a disk typically organized?
As a one-dimensional linear array of logical blocks mapped onto sectors, with Sector 0 being the first sector
5What is the responsibility of the operating system regarding disk drives?
To use hardware efficiently, especially disk drives
6What are the main criteria for disk drivers?
Fast access time and increased disk bandwidth
7What are the two components of disk access time?
Seek time and rotational latency
8What is seek time?
Time for the disk arm to move to the head of the cylinder containing the desired sector
9What is rotational latency?
Additional time waiting for the disk to rotate to the desired sector under the disk head
10How is disk bandwidth defined?
Total number of bytes transferred divided by the total time between the first request for service and the computation of the last transfer
11Why does the OS schedule disk I/O requests in a particular order?
To improve access time and bandwidth
12What happens when a process needs I/O from the disk?
System calls are issued to the OS; if the disk is available, the request is serviced, otherwise it is queued
13What is the main aim of disk scheduling algorithms?
To reduce seek time and rotational latency while increasing bandwidth
14Name the main disk scheduling algorithms.
FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK
15What is the simplest disk scheduling algorithm?
First Come First Serve (FCFS)
16What are the characteristics of FCFS?
Simplest, fair, does not provide the fastest service, requests serviced in order of arrival
17What is the main principle of Shortest Seek Time First (SSTF)?
Services the request closest to the current head position to minimize seek time
18What is the disadvantage of SSTF?
Requests far from the head may wait a long time, leading to starvation
19How does SCAN (Elevator Algorithm) work?
The disk arm moves from one end to the other, servicing requests along the way, then reverses direction
20What is the disadvantage of SCAN?
Requests just missed by the head must wait until the arm moves to the other end and back
21How does C-SCAN differ from SCAN?
C-SCAN moves in one direction, jumps to the opposite end without servicing during the jump, then continues servicing in the same direction
22How does LOOK differ from SCAN?
LOOK stops at the last request in its direction rather than going to the physical end of the disk
23How does C-LOOK differ from C-SCAN?
C-LOOK stops at the last request in its direction before jumping to the last request on the other side, rather than going to the physical end
24What are the similarities between SCAN and LOOK?
Both service requests in one direction and then reverse
25What is the main difference between SCAN and LOOK?
SCAN goes to the end of the disk before reversing, LOOK stops at the last request in the direction
26What are the similarities between C-SCAN and C-LOOK?
Both move in one direction, jump back without servicing during the jump, and then service requests again while moving forward
27What is the difference between C-SCAN and C-LOOK?
C-SCAN goes to the physical end before jumping back, C-LOOK stops at the last request before jumping to the opposite end
28What is the formula to calculate total seek time in disk scheduling?
Total Seek Time = Sum of absolute differences between consecutive head positions, i.e., Total Seek Time = Σ |Current Head Position - Next Request|