Disk structure and access time in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Disk Access Components

Which of the following components primarily determines the seek time when accessing data on a disk?

A The time taken to transfer data from the disk to memory

B The time taken for the disk arm to move to the correct track

C The time taken for the disk to rotate to the correct sector

D The time taken by the CPU to process the data

💡 Hint

Seek time is related to the movement of the disk's mechanical parts.

Seek time is the time required for the disk arm to move the read/write head to the track where the data is stored. It depends on the mechanical movement of the arm.

📋 Factual

intermediate

Components of Disk Access Time

Which of the following correctly lists the three main components of disk access time?

A Seek time, rotational latency, data transfer time

B CPU time, seek time, data transfer time

C Rotational latency, CPU time, memory access time

D Data transfer time, CPU time, network latency

💡 Hint

Think about the mechanical and data movement delays involved in reading from a disk.

Disk access time is made up of seek time (moving the arm), rotational latency (waiting for the sector to rotate under the head), and data transfer time (moving data to memory).

🔍 Analysis

advanced

Calculating Average Rotational Latency

A disk rotates at 7200 revolutions per minute (RPM). What is the average rotational latency in milliseconds?

A 16.67 ms

B 8.33 ms

C 2.08 ms

D 4.17 ms

💡 Hint

Average rotational latency is half the time for one full rotation.

One rotation time = 60 seconds / 7200 = 0.00833 seconds = 8.33 ms. Average latency is half of that = 4.17 ms.

❓ Comparison

advanced

Comparing Access Times of SSD and HDD

Which statement best explains why SSDs generally have faster access times than HDDs?

A SSDs spin faster than HDDs, reducing rotational latency

B SSDs have slower data transfer rates but faster CPU processing

C SSDs have no moving parts, eliminating seek time and rotational latency

D SSDs use larger platters to store data, increasing transfer speed

💡 Hint

Think about the mechanical differences between SSDs and HDDs.

SSDs use flash memory with no moving parts, so they do not have seek time or rotational latency, making access faster than HDDs which rely on mechanical movement.

❓ Reasoning

expert

Effect of Disk Scheduling on Access Time

Consider a disk scheduling algorithm that minimizes seek time by reordering requests. Which of the following is a likely effect of this algorithm on overall disk access time?

A It reduces average seek time but may increase wait time for some requests

B It increases rotational latency by randomizing request order

C It eliminates data transfer time by preloading data

D It increases CPU processing time without affecting disk access

💡 Hint

Think about trade-offs when reordering disk requests to reduce arm movement.

Disk scheduling algorithms like SSTF reduce average seek time by reordering requests, but some requests may wait longer, increasing their individual wait times.