AP Computer Science Principles Quiz: Fault Tolerance
20 questions · exam conditions
0:00
Fault ToleranceQuestion 1 of 20

A local area network (LAN) is set up with two switches. All computers are connected to the first switch. The second switch is kept in a closet as a spare, ready to be installed if the first one fails.

How does this setup differ from a truly fault-tolerant system?

A fault-tolerant system would use a single, more reliable switch instead of two.
In a fault-tolerant system, the backup switch would be automatically and instantly activated upon failure, without manual intervention.
A fault-tolerant system would not require switches and would connect all computers directly to each other.
In a fault-tolerant system, the backup switch would be from a different manufacturer to avoid common bugs.
← Back to quizzes

AP Computer Science Principles Quiz

AP Computer Science Principles Quiz: Fault Tolerance

Practice Fault Tolerance in AP Computer Science Principles with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Fault Tolerance, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Computer Science Principles.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A local area network (LAN) is set up with two switches. All computers are connected to the first switch. The second switch is kept in a closet as a spare, ready to be installed if the first one fails.

How does this setup differ from a truly fault-tolerant system?

  1. A fault-tolerant system would use a single, more reliable switch instead of two.
  2. In a fault-tolerant system, the backup switch would be automatically and instantly activated upon failure, without manual intervention. (correct answer)
  3. A fault-tolerant system would not require switches and would connect all computers directly to each other.
  4. In a fault-tolerant system, the backup switch would be from a different manufacturer to avoid common bugs.

Explanation: Having a spare part is a form of redundancy, but fault tolerance implies the system can handle the failure automatically with minimal or no downtime. This setup, known as a cold spare, requires manual intervention and results in system downtime, whereas a hot spare in a truly fault-tolerant system would take over automatically.

Question 2

A small business relies on a single Internet connection from one service provider. The owner is concerned that if this provider has an outage, the business will be unable to process online orders.

To best improve the fault tolerance of the business's Internet access, which action should be taken?

  1. Upgrade the existing Internet connection to a higher bandwidth plan.
  2. Purchase a second, separate Internet connection from a different service provider. (correct answer)
  3. Install a new, more powerful router to replace the one provided by the current provider.
  4. Set up a local server to cache frequently visited websites to reduce Internet usage.

Explanation: This action introduces redundancy for the entire Internet connection. If the primary provider has an outage, the business can switch to the secondary provider, thus continuing operations. This directly addresses the single point of failure.

Question 3

The original design motivation for the network that became the Internet included the need for a communication system that could withstand a large-scale disaster. This motivation directly led to which core principle?

  1. High-speed data transfer
  2. Fault tolerance (correct answer)
  3. Data encryption
  4. Open protocols

Explanation: The need for a network that could survive the loss of some of its nodes is the very definition of fault tolerance. This foundational requirement shaped the Internet's decentralized, packet-switched architecture with redundant paths.

Question 4

A large social media platform experiences a software bug that causes one of its image-hosting servers to crash. However, users are still able to view and upload images without interruption. Which of the following is the most likely explanation for this?

  1. The platform has a fault-tolerant design with multiple redundant servers, and traffic was automatically rerouted to working servers. (correct answer)
  2. The users' web browsers had cached all the images, so they did not need to connect to the server.
  3. The platform's protocol automatically fixed the software bug on the crashed server and restarted it instantly.
  4. The platform uses a lossless compression algorithm, which reduces the load on the servers and prevents them from crashing.

Explanation: This scenario describes a classic case of fault tolerance in action. The failure of a single component (one server) did not cause a failure of the entire system because redundant components (other servers) were available to take over its workload.

Question 5

A home security company monitored sensors over a wireless network. Sometimes interference flipped bits in a message, so the system added a small check value to each packet. If the check did not match, the receiver requested the packet again, and the correct alert was delivered. This kept door and window events accurate even on noisy nights. In the example given, how does the described system maintain functionality during a failure?

  1. It encrypted data to hide sensor names
  2. It detected errors and requested resend (correct answer)
  3. It boosted volume so alerts sounded louder
  4. It deleted packets to prevent delays

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the system uses error detection and correction by adding check values to packets and requesting retransmission when errors are detected. Choice B is correct because it accurately describes how the system detects errors through check values and requests resending of corrupted packets. Choice A is incorrect because encryption is about security and privacy, not error detection - the passage specifically mentions detecting bit flips from interference. To help students, emphasize the difference between error detection (finding mistakes) and other fault tolerance mechanisms. Practice identifying checksum/parity concepts and how they enable reliable communication over unreliable channels.

Question 6

A cloud storage service ran on a primary server and a backup server in different data centers. When the primary server crashed during peak use, the system automatically switched users to the backup within seconds, and most people kept uploading files without noticing. The service logged the failure and later repaired the primary server, then restored it as the main system. Based on the scenario described, in the scenario, what role does Failover play?

  1. It split traffic evenly to speed uploads
  2. It switched service to a backup server (correct answer)
  3. It permanently shut down the service
  4. It reduced file sizes before sending

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the system uses automatic failover to maintain functionality when the primary server crashes, switching users to a backup server within seconds. Choice B is correct because it accurately reflects how the system automatically switched service to the backup server when the primary failed, which is the definition of failover. Choice A is incorrect because it describes load balancing, not failover - the system didn't split traffic evenly but rather redirected all traffic to the backup. To help students, emphasize that failover specifically involves switching from a failed component to a working backup, not distributing load. Practice identifying the difference between failover (switching to backup) and load balancing (distributing work).

Question 7

A large data center hosted websites for local hospitals. To keep services available, the building used 2 power feeds from different utility lines. If both feeds dropped, battery units kept the servers running long enough for diesel generators to start. During a storm, one utility line failed, but the servers stayed online because the other feed continued providing electricity. Later that night, the second line flickered and the batteries bridged the gap until the generator took over. Staff reported that patients could still access appointment pages the entire time. In the example given, what is the primary benefit of using Redundancy as illustrated in the passage?

  1. It reduces the price of electricity
  2. It keeps services available during outages (correct answer)
  3. It speeds up website loading every day
  4. It prevents any component from failing

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the system uses multiple layers of redundancy including two power feeds, battery units, and diesel generators to maintain continuous power supply. Choice B is correct because it accurately identifies that redundancy keeps services available during outages, as demonstrated when the hospital websites remained accessible throughout the storm. Choice D is incorrect because redundancy doesn't prevent failures but rather ensures continued operation despite failures. To help students, emphasize that redundancy provides backup options rather than preventing failures entirely. Watch for: confusion between prevention and mitigation strategies, and overgeneralization about what redundancy can achieve.

Question 8

A small business hosted its website in a cloud service with 2 regions. The website ran in Region 1, but Region 1 had an outage. The cloud provider redirected requests to Region 2 automatically, and customers still browsed products. Later, the provider restored Region 1 and returned traffic gradually. Based on the scenario described, which mechanism ensures system operation when a component fails?

  1. Automatic Failover to another region (correct answer)
  2. Manual typing of each customer request
  3. Extra animations to keep users engaged
  4. A larger logo to improve brand recall

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the cloud service uses automatic failover between regions - when Region 1 has an outage, the provider automatically redirects requests to Region 2. Choice A is correct because it accurately identifies automatic failover as the mechanism that maintains service by switching from the failed region to a working region. Choice B is incorrect because manual typing of requests would be inefficient and doesn't relate to automated fault tolerance mechanisms. To help students, emphasize that cloud providers often use geographic redundancy with automatic failover between regions. Practice identifying how DNS redirection and load balancers enable seamless regional failover.

Question 9

An online store ran its checkout service on 2 servers: one active and one standby. When the active server's disk failed, the standby server took over the same network address and continued processing carts. Customers mostly saw no interruption, and orders still completed. The failed disk was replaced later and the standby returned to waiting mode. In the example given, in the scenario, what role does Failover play?

  1. It switched checkout to the standby server (correct answer)
  2. It compressed images to load pages faster
  3. It prevented any server from ever failing
  4. It caused checkout to stop until repairs

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the system uses failover when the active server's disk fails - the standby server takes over the same network address and continues processing. Choice A is correct because it accurately describes the failover process where checkout switched from the failed active server to the standby server. Choice C is incorrect because failover doesn't prevent failures from occurring; it provides a mechanism to continue operating when failures do happen. To help students, emphasize that failover involves automatic switching to backup systems when primary systems fail. Practice identifying active-standby configurations and how they maintain service continuity.

Question 10

A delivery company sent route updates from trucks to headquarters over a cellular network. Some messages arrived with mistakes due to weak signal. Each message included extra bits that helped the receiver spot an error and rebuild the original data, so dispatch still saw correct locations. This kept tracking reliable without calling drivers repeatedly. Based on the scenario described, which mechanism ensures system operation when a component fails?

  1. Error detection and correction in messages (correct answer)
  2. Load balancing across multiple web pages
  3. Adding more drivers to reduce traffic
  4. Turning off updates to avoid wrong data

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the system uses error detection and correction through extra bits that help spot errors and rebuild original data when messages are corrupted by weak signals. Choice A is correct because it accurately identifies error detection and correction as the mechanism that ensures reliable communication despite transmission errors. Choice B is incorrect because load balancing distributes work across resources, which is different from correcting transmission errors in messages. To help students, emphasize that error correction codes allow systems to recover from data corruption without retransmission. Practice identifying different error handling strategies: detection only vs. detection and correction.

Question 11

A large e-commerce company wants to ensure its website remains available to customers even if one of its data centers experiences a complete power outage. The company currently operates a single, large data center.

Which of the following strategies would be most effective for making the company's website fault-tolerant with respect to a power outage?

  1. Installing more powerful servers within the existing single data center to handle traffic more efficiently.
  2. Increasing the bandwidth of the Internet connection to the single data center to allow for faster data transfer.
  3. Creating a complete, mirrored copy of the website and its database in a separate data center in a different geographic location. (correct answer)
  4. Implementing a more complex password policy for customer accounts to improve overall system security.

Explanation: This strategy introduces redundancy at a large scale. If one data center fails (due to a power outage or other issue), the system can redirect traffic to the mirrored site in the other location, allowing the service to continue functioning.

Question 12

A network is configured in a star topology, where all devices are connected to a single central switch. Data sent from one device to another must pass through this central switch.

What is the greatest vulnerability of this network design from a fault-tolerance perspective?

  1. If one of the connected devices fails, it may disrupt traffic for all other devices on the network.
  2. The central switch represents a single point of failure; if it malfunctions, the entire network will cease to function. (correct answer)
  3. The network's performance will decrease significantly as more devices are added and communicate simultaneously.
  4. Data packets can collide if two devices attempt to send data at the exact same time through the switch.

Explanation: In a star topology, the central switch is a critical component. Its failure will disconnect all devices from each other, making it a single point of failure and a major vulnerability for fault tolerance.

Question 13

A hospital maintains its critical patient records in a database. To ensure the data is always accessible, the system automatically saves a copy of the database to a backup server in the same building every hour.

While this system has some redundancy, it is still vulnerable to which of the following failures?

  1. A failure of the main database server's hard drive, which would cause temporary data inaccessibility.
  2. A localized event like a fire or building-wide power outage that affects both servers simultaneously. (correct answer)
  3. A software bug that corrupts a single patient record on the main server before the hourly backup.
  4. A slow network connection between the main server and the backup server, delaying the copy process.

Explanation: Keeping the backup server in the same building means that a single, localized disaster could destroy both the primary and backup systems. This identifies a vulnerability where the redundancy is insufficient to protect against a large-scale failure affecting the entire location.

Question 14

A system is designed with a single, powerful firewall that inspects all incoming and outgoing network traffic. No traffic can enter or leave the network without passing through this device.

From a fault tolerance perspective, what is the primary drawback of this design?

  1. The firewall may require frequent software updates to protect against new security threats.
  2. The firewall could slow down network communication for all users due to the inspection process.
  3. The firewall is a single point of failure; its malfunction would sever the network's connection to the outside. (correct answer)
  4. The firewall might incorrectly block legitimate traffic, preventing users from accessing needed resources.

Explanation: Relying on a single device for a critical function like connectivity creates a single point of failure. If the firewall fails, the entire network's ability to communicate externally is lost, which is a major fault tolerance weakness.

Question 15

When a message is sent over the Internet, it is broken into packets. If a network path becomes congested or fails after some packets have been sent, what typically happens to the remaining packets of the message?

  1. The remaining packets are discarded, and the sender must retransmit the entire message from the beginning.
  2. The network's routing protocols will attempt to send the remaining packets along a different, available path. (correct answer)
  3. The packets are held at the last successful router until the original path is repaired and becomes available again.
  4. The sender's computer automatically compresses the remaining packets to push them through the congested path.

Explanation: This is a core feature of the Internet's fault-tolerant design. Because each packet is routed independently, the network can adapt to failures in real-time by finding alternative routes for subsequent packets.

Question 16

An online service provider's infrastructure is described as having high scalability.

How is the concept of scalability different from the concept of fault tolerance?

  1. Scalability is the ability to handle an increasing amount of work, while fault tolerance is the ability to withstand component failures. (correct answer)
  2. Scalability refers to the physical size of the data centers, while fault tolerance refers to the software used on the servers.
  3. Scalability is the measure of network speed, while fault tolerance is the measure of system security against attacks.
  4. Scalability is achieved through data compression, while fault tolerance is achieved through data encryption.

Explanation: The two concepts are distinct but related. Scalability is about handling growth in load or traffic, often by adding resources. Fault tolerance is about ensuring continued operation when parts of the system fail. A system can be scalable but not fault-tolerant, and vice-versa.

Question 17

A city's emergency alert system sent short messages from a central office to many radio towers. Because messages traveled through noisy links, a few packets occasionally arrived with altered bits. Each packet included extra information that let the receiver notice a mismatch. When a mismatch appeared, the receiver corrected small errors when possible; otherwise it requested the packet again. This helped ensure that evacuation notices were not changed into confusing text. During a thunderstorm, the system still delivered accurate alerts to most towers. In the example given, which mechanism ensures system operation when a component fails?

  1. Error detection and correction keeps data accurate (correct answer)
  2. Load balancing spreads users across servers
  3. A faster antenna prevents all interference
  4. Turning off the network avoids wrong messages

Explanation: This question tests AP Computer Science Principles skills, specifically understanding fault tolerance in computing systems and networks. Fault tolerance is the ability of a system to continue operating properly in the event of a failure of some of its components. It involves mechanisms like redundancy, error detection and correction, and failover. In the passage, the emergency alert system uses error detection and correction to identify and fix corrupted bits in messages, ensuring accurate delivery of critical information. Choice A is correct because it accurately identifies error detection and correction as the mechanism that keeps data accurate despite noisy transmission links. Choice C is incorrect because it suggests preventing interference entirely, which is impossible in real-world conditions as shown by the thunderstorm scenario. To help students, emphasize that error detection and correction handles data corruption, not component failures. Watch for: confusion between different fault tolerance mechanisms and unrealistic expectations about preventing all errors.

Question 18

Which of the following best explains how packet switching supports a fault-tolerant network?

  1. It establishes a dedicated, fixed circuit between two communicating devices, guaranteeing the connection quality.
  2. It ensures all packets in a message arrive in the correct sequence by numbering them before transmission.
  3. It allows each data packet to be routed independently, enabling the network to bypass failed or congested links. (correct answer)
  4. It bundles data from multiple users into a single packet to maximize the use of the network's bandwidth.

Explanation: The independent routing of packets is key. Unlike circuit switching, which uses a fixed path, packet switching allows the network to be flexible and adaptive. If one path fails, only the packets currently on that path are lost; subsequent packets can be sent on working routes.

Question 19

Which of the following scenarios best illustrates the concept of redundancy in a computing system?

  1. A user protects their account with a password and a fingerprint scan.
  2. A file is compressed to a smaller size before being sent over a network.
  3. An airline's booking system runs on identical servers in two geographically separate locations. (correct answer)
  4. A program is broken into smaller tasks that can be run simultaneously on multiple processors.

Explanation: This is a clear example of redundancy for fault tolerance. The identical servers are duplicate components. If one location fails, the other can take over, ensuring the booking system remains available.

Question 20

Which of the following statements best describes a fault-tolerant computer system?

  1. A system designed to prevent any and all component failures from occurring through rigorous testing.
  2. A system that can continue to function, potentially at a reduced level, even when one or more of its components fail. (correct answer)
  3. A system optimized to perform computations at the highest possible speed, minimizing processing time.
  4. A system that uses advanced encryption to protect itself from all types of unauthorized access and cyberattacks.

Explanation: Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of some of its components. It does not prevent failures but allows the system to cope with them.