How many levels of client-server architectures do you know?

Three.

Single-tier: there is no separation between client and server, all logic and data are on one node.

Two-tier:

• Thin client: All logic is executed on the server, the client only displays data.
• Thick client: The main logic is executed on the client, the server is used for data storage and performing specific operations.

Three-tier:

• Client tier (Presentation Tier): User interface.
• Business logic tier (Application Tier / Business Logic Tier): Data processing, rule execution.
• Data tier: Storage and management of data.

Multi-tier (N-tier): An extension of the three-tier architecture, where the business logic can be divided into several sub-tiers.