C-SCAN (circular SCAN) in Operating Systems - Mini Project: Build & Apply

C-SCAN Disk Scheduling Algorithm Simulation

📖 Scenario: You are working in an operating system team. You need to simulate the C-SCAN disk scheduling algorithm to understand how it manages disk head movement for servicing requests efficiently.

🎯 Goal: Build a Python program that simulates the C-SCAN disk scheduling algorithm. The program will take a list of disk requests and the initial head position, then calculate the order in which requests are serviced and the total head movement.

📋 What You'll Learn

Create a list called requests with exact disk request positions: 95, 180, 34, 119, 11, 123, 62, 64

Create an integer variable called head with the initial head position 50

Create an integer variable called disk_size with the value 200 representing the total number of cylinders

Implement the C-SCAN algorithm logic to service requests in one direction and then jump to the start

Calculate the total head movement in servicing all requests

💡 Why This Matters

🌍 Real World

Disk scheduling algorithms like C-SCAN are used in operating systems to reduce the time the disk head spends moving between requests, improving performance.

💼 Career

Understanding disk scheduling is important for roles in system programming, OS development, and performance optimization.

1

Create the initial data setup

Create a list called requests with these exact values: 95, 180, 34, 119, 11, 123, 62, 64. Also create an integer variable called head and set it to 50.

Operating Systems

# Create the list of disk requests and initial head position
# Your code here

Need a hint?

Use a Python list for requests and assign the exact numbers. Use a simple integer variable for head.

2

Add disk size configuration

Create an integer variable called disk_size and set it to 200 to represent the total number of cylinders on the disk.

Operating Systems

requests = [95, 180, 34, 119, 11, 123, 62, 64]
head = 50
# Create disk_size variable
# Your code here

Need a hint?

Use a simple integer variable named disk_size and assign 200.

3

Implement the C-SCAN algorithm logic

Write code to implement the C-SCAN algorithm: sort the requests, split them into two lists based on the head position, service requests moving upwards, then jump to the start (0), and service remaining requests. Store the service order in a list called seek_sequence.

Operating Systems

requests = [95, 180, 34, 119, 11, 123, 62, 64]
head = 50
disk_size = 200
# Implement C-SCAN logic and create seek_sequence list
# Your code here

Need a hint?

Sort the requests, split into two lists by comparing with head, then append requests from right list, add the jump to end and start, then append left list requests.

4

Calculate total head movement

Calculate the total head movement by summing the absolute differences between the head and the first request in seek_sequence, then between each consecutive request in seek_sequence. Store the result in a variable called total_movement.

Operating Systems

requests = [95, 180, 34, 119, 11, 123, 62, 64]
head = 50
disk_size = 200

requests.sort()

left = [r for r in requests if r = head]

seek_sequence = []

# Service requests on the right of head
for r in right:
    seek_sequence.append(r)

# Jump to the start (0) after reaching the end
seek_sequence.append(disk_size - 1)  # Move to the last cylinder
seek_sequence.append(0)  # Jump to the first cylinder

# Service requests on the left of head
for r in left:
    seek_sequence.append(r)

# Calculate total head movement
# Your code here

Need a hint?

Start from head, add the absolute difference to each request in seek_sequence to total_movement.