SCAN (elevator algorithm) in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to describe the direction of the SCAN algorithm.

Operating Systems

The SCAN algorithm moves the disk arm in one [1] until it reaches the end of the disk.

Drag options to blanks, or click blank then click option'

Atrack

Bspeed

Cqueue

Ddirection

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'direction' with 'speed' or 'track'.

Thinking the arm moves randomly instead of in a set direction.

The SCAN algorithm moves the disk arm in one direction servicing requests until it reaches the end of the disk.

2fill in blank

medium

Complete the code to explain what happens after the SCAN algorithm reaches the last request in one direction.

Operating Systems

After reaching the end of the disk in one direction, the disk arm [1] and starts servicing requests in the opposite direction.

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Areverses

Bstops permanently

Caccelerates

Dignores

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming the arm stops permanently after reaching the end.

Thinking the arm accelerates instead of reversing.

After reaching the end of the disk in one direction, the disk arm reverses and starts servicing requests in the opposite direction.

3fill in blank

hard

Fix the error in the description of the SCAN algorithm's movement.

Operating Systems

The SCAN algorithm moves the disk arm in one direction to service requests, reversing direction at the end of the disk. This is called [1].

Drag options to blanks, or click blank then click option'

ALOOK

BFCFS

CSCAN

DC-SCAN

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing SCAN with FCFS which is first-come, first-served.

Mixing SCAN with LOOK or C-SCAN algorithms.

The SCAN algorithm moves the disk arm in one direction servicing requests and reverses direction at the disk's end. It is also called the elevator algorithm.

4fill in blank

hard

Fill both blanks to complete the SCAN algorithm's behavior description.

Operating Systems

The SCAN algorithm services requests by moving the disk arm towards the [1] end, then reverses direction at the [2] end.

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Astart

Bmiddle

Cend

Drandom

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'middle' or 'random' instead of 'start' or 'end'.

Not understanding the arm reverses at the disk's physical ends.

The SCAN algorithm moves the disk arm towards the start end of the disk, then reverses direction at the end end, servicing requests along the way.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension describing SCAN's request servicing.

Operating Systems

serviced = {track: requests[track] for track in range([1], [2], [3]) if track in requests}

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Astart_track

Bend_track

Cstep

Drandom_track

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'random_track' which is not valid for range.

Mixing up start and end positions or forgetting the step.

This comprehension collects requests from start_track to end_track moving by step (which can be +1 or -1 depending on direction) to simulate SCAN's servicing order.