Two-Tier and Three-Tier Architecture

1. Two-Tier Architecture

In Two-Tier architecture, the client application communicates directly with the database server. There is no separate application layer.

Client Application
        |
        |
Database Server
(DBMS + Database)

• Client handles UI and some business logic
• Database server stores and processes data
• Used in small-scale systems

2. Advantages of Two-Tier Architecture

• Simple design
• Fast communication
• Easy to develop

3. Disadvantages of Two-Tier Architecture

• Limited scalability
• Low security
• Heavy load on database server

4. Three-Tier Architecture

In Three-Tier architecture, the application is divided into three separate layers: presentation, application logic, and database.

Client (Presentation Layer)
          |
Application Server
 (Business Logic Layer)
          |
Database Server
   (DBMS + Database)

• Client handles user interface only
• Application server processes logic
• Database server stores data

5. Advantages of Three-Tier Architecture

• High scalability
• Better security
• Easy maintenance
• Load balancing support

6. Disadvantages of Three-Tier Architecture

• Complex design
• Higher development cost
• Slower than two-tier in small systems

7. Two-Tier vs Three-Tier Architecture

Feature            Two-Tier               Three-Tier
----------------   --------------------   ------------------------
Layers             2                      3
Scalability        Low                    High
Security           Low                    High
Maintenance        Difficult              Easy
Usage              Small applications     Web & enterprise apps

8. Real-Life Examples

• Two-Tier → Desktop banking system
• Three-Tier → E-commerce websites
• Three-Tier → Online learning platforms

Practice Questions

1. Explain two-tier architecture with diagram.
2. Explain three-tier architecture with diagram.
3. List advantages of three-tier architecture.
4. Differentiate between two-tier and three-tier architecture.

Practice Task