Two marks Questions with Answers

Two Marks Questions with Answers

Q.1 List out any two disk scheduling techniques.

Ans. Disk scheduling techniques are FCFS, SSTF, SCAN and C-SCAN. 

Q.2 Define seek-time and latency time for a hard-disk (HDD) mechanism

Ans.Latency time: It is the time spent waiting for the target sector to appear under the read and write head.

Q.3 Seek time: Seek time is the time required to move the disk arm to the required 

Q.4 In the context of disk reliability define mirroring.

Ans. A mirror set comprises two equal sized partitions on two disks. When an application writes data to a mirror set, FtDisk writes contents of the two partitions are identical.

Q.5 What is the need for disk scheduling ?

Ans. For a multiprogramming system with many processes, the disk queue may often have several pending requests. Thus, when one request is completed, the OS chooses which pending request to service next. To reduce seek time and increase disk bandwidth, disk scheduling is required.

Q.6 Why is rotational latency usually not considered in disk scheduling ?

Ans. It is additional time waiting for the disk to rotate the desired sector to the disk head.

Q.7 What is rotational latency?

Ans. The time to wait for the target sector to rotate underneath the head.

Q.8 What is a swap space?ells

Ans.

Secondary memory is swap device and the section of disk used for this purpose is known as swap space.

Q.9 Write the three basic functions which are provided by the hardware clocks and timers.

Ans. Three basic functions are :

1. Give the current time.

2. Give the elapsed time.

3. Set a timer to trigger operation X at time T.

Q.10 What are seek time and rotational latency ?

Ans: Seek time: It is a time required to move the disk arm to the required track. Rotational latency: It is time spent waiting for the target sector to appear under the read and write heads.

Q.11 Define mirroring and shadowing.

Ans: Mirroring: Mirroring is the replication of logical disk volumes onto separate physical hard disks in real time to ensure continuous availability. Mirroring is also called shadowing.

Q.12 Which disk scheduling algorithm would be best to optimize the performance of a RAM disk ?

Ans. : RAM disk has uniform access times. So all disk scheduling algorithm gives same effect.

Q.13 Writable CD-ROM media are available in both 650 MB and 700 MB versions. What is the principle disadvantage, other than cost, of the 700 MB version ?

Ans.Limited space is disadvantage of 700 MB versions.

Q.14 What characteristics determine the disk access speed?

Ans.Rotational delay and seek time.

Q.15 Give the importance of swap-space management.

Ans. Importance of swap space management is to provide the best throughput for the virtual memory system.

Q.16 Explain difference between latency and throughput. du

Ans. Latency is defined as the time required processing a single instruction, while throughput is defined as the number of instructions processed per second.

Q.17 What is cylinder ?

Ans. Cylinder is used to refer to all the tracks under the arms at a given points on all surfaces.

Q.18 What is bandwidth ?

Ans. The maximum amount of information that can be transferred to or from the memory per unit time is called bandwidth.

Q.19 Define constant linear velocity.

Ans. The Constant Linear Velocity (CLV) format optimizes utilization of the usable recording area by having an uniform recording density throughout the disk. By maintaining the linear velocity constant, the recording density is kept constant. Data are stored in one continuous track that spirals from the circumference inwards to the centre. As the tracks moves inwards, the radius decreases and to maintain the same linear velocity the disk must spin faster.

Q.20 What is SCAN disk scheduling ?

Ans. The disk arm starts at one end of the disk, and moves toward the other end, servicing requests until it gets to the other end of the disk, where the head movement is reversed and servicing continues.

Q.21 What are the two major components of access time ?

 Ans. Two components are:

a. Seek time is the time for the disk are to move the heads to the cylinder containing the desired sector.

b. Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.

Q.22 What is the difference between block-oriented devices and stream-oriented devices?

Ans. Block-oriented devices stores information in blocks that are usually of fixed size, and transfers are made one block at a time. Generally, it is possible to reference data by its block number. Disks and tapes are examples of block-oriented devices. Stream-oriented devices transfer data in and out as a stream of bytes, with no block structure. Terminals, printers, communications ports, mouse and other pointing devices, and most other devices that are not secondary storage are stream oriented.

Q.23 What are the device drivers ?

Ans. A device driver is a program that controls a particular type of device that is attached to your computer. There are device drivers for printers, displays, CD-ROM readers, diskette drives and so on.

Q.24 What is tertiary storage ?

Ans. Tertiary storage is built from disk and tape drives that use removable media. Low cost is the defining characteristic of tertiary storage.

Q.25 What is trap?

Ans. A trap is a software generated interrupt caused either by an error or by a specific request from a user program that an operating system service be performed.

Q.26 What do you mean by WORM disk ?

Ans. WORM means "Write Once, Read Many Times" disks can be written only once. Thin aluminum film sandwiched between two glass or plastic platters. To write a bit, the drive uses a laser light to burn a small hole through the aluminum; information can be destroyed by not altered.

Q.27 Give the various disk scheduling methods.

Ans.1. FCFS 2. SSTF 3. SCAN 4. C-SCAN 5. LOOK 6. C-LOOK.

Q.28 What is HSM? Where it is used?

Ans. Hierarchical Storage Management (HSM) is a data storage techniques automatically moves data between high-cost and low-cost storage media. HSM systems store the bulk of the enterprise's data on slower devices and then copy data to faster disk drives when needed.

Q.29 How does DMA increase system concurrency?

Ans. DMA increases system concurrency by allowing the CPU to perform tasks while the DMA system transfers data via the system and memory buses.

Q.30 Define C-SCAN scheduling.

Ans.Head begins its scan toward the nearest end and works it way all the way to the end of the system. Once it hits the bottom or top it jumps to the other end and moves in the same direction

Q.31 Why is it important to scale up system-bus and device speeds as CPU speed increases ?

Ans. Consider a system which performs 50 % I/O and 50 % computes. Doubling the CPU performance on this system would increase total system performance by only 50 %. Doubling both system aspects would increase performance by 100 %. Generally, it is important to remove the current system bottleneck and to increase overall system performance rather than blindly increasing the performance of individual system components.

Q.32 Suppose that the disk rotates at 7200 RPM. What is the average rotational latency of this disk drive? AU CSE: May-17

Ans. Disk rotates at 7200 rpm which gives 120 rotations per second. One rotation = 60s / 7200 = 8.33 ms Thus, a full rotation takes 8.33 ms and the average rotational latency (a half rotation) takes 4.167 ms.

Q.33 What is SSD?

Ans. Solid State Disks (SSD) is a storage device that is based on semiconductors rather than rotating magnetic platters. It uses serial ATA or IDE interface as hard drives. Most SSDs are based on NAND flash chips.