What is the difference between functional and non-functional requirements?

Question

Accepted Answer

**Functional** — what system does. **Non-functional** — how system performs.

**Functional requirements:**
- Define system behavior.
- What the system should do.
- Features and functionality.
- User interactions.

```
Examples:
- User can login with email/password
- System sends email confirmation
- User can search for products
```

**Non-functional requirements:**
- Define system qualities.
- How the system should perform.
- Performance, security, usability.
- Constraints and standards.

```
Examples:
- Page loads in under 2 seconds
- System supports 10,000 concurrent users
- Data encrypted with AES-256
```

**Key differences:**
- **Functional** — features, what.
- **Non-functional** — qualities, how.

Business Analyst: What is the difference between functional and non-functional requirements?