Explain what the CAP theorem is and how it influences the choice of architecture for distributed systems.

The CAP theorem states that in a distributed system, it is impossible to simultaneously guarantee three properties:

• Consistency: All nodes see the same data at the same time.
• Availability: Every request receives a response (successful or error) without guarantee of data freshness.
• Partition tolerance: The system continues to operate despite network splits.

During network partitions, the system must choose between consistency and availability. This affects architecture:

• If consistency is crucial (e.g., banking transactions), CP systems are chosen, which may sacrifice availability.
• If availability is crucial (e.g., social networks), AP systems are chosen, where data may be temporarily inconsistent.

Understanding CAP helps in designing distributed systems considering data requirements and fault tolerance.