🍪 Cookies and Sessions (Web Engineering)
📌 1. Definition
🍪 Cookies
A cookie is a small piece of data stored in the user’s browser by a website to remember information about the user.
🔐 Sessions
A session is a server-side mechanism used to store user data temporarily on the server during a user’s interaction with a website.
🎯 2. Key Difference Idea
Cookies → Stored in Browser (Client-side)
Sessions → Stored on Server (Server-side)
🍪 3. Cookies
📌 3.1 How Cookies Work
Browser → Request → Server
Server → Sends Cookie → Browser stores it
Next request → Cookie sent back automatically
🧠 3.2 Characteristics of Cookies
- Stored in browser
- Small size (about 4KB)
- Can expire
- Sent with every HTTP request
⚙️ 3.3 Types of Cookies
1. Persistent Cookies
- Stored for a long time
- Have expiration date
2. Session Cookies
- Deleted when browser closes
💡 3.4 Example (PHP Cookie)
setcookie("user", "Ali", time() + 3600);
📈 3.5 Advantages of Cookies
- Remember user preferences
- Faster login experience
- Personalized content
❌ 3.6 Disadvantages of Cookies
- Security risks
- Limited storage
- Can be deleted by user
🔐 4. Sessions
📌 4.1 How Sessions Work
User → Login → Server creates Session ID
Server stores data → Browser stores Session ID only
🧠 4.2 Characteristics of Sessions
- Stored on server
- More secure than cookies
- Ends when user logs out or times out
- Uses Session ID
⚙️ 4.3 Example (PHP Session)
session_start();
$_SESSION["user"] = "Ali";
📈 4.4 Advantages of Sessions
- More secure
- Stores large data
- Controlled by server
❌ 4.5 Disadvantages of Sessions
- Uses server memory
- Can slow down server with many users
- Ends after timeout
🔄 5. Cookies vs Sessions (Very Important)
| Feature |
Cookies 🍪 |
Sessions 🔐 |
| Storage |
Browser |
Server |
| Security |
Less secure |
More secure |
| Size |
Small (4KB) |
Large |
| Expiry |
Can be set |
Ends on logout/time |
| Speed |
Faster |
Slightly slower |
| Control |
Client-side |
Server-side |
📊 6. Working Diagram (Exam Use)
Cookies:
User ↔ Browser ↔ Server
Sessions:
User ↔ Browser (Session ID) ↔ Server (Stores Data)
⚠️ 7. Important Points
✔ Cookies store user preferences
✔ Sessions store sensitive data
✔ Cookies are less secure
✔ Sessions are more secure
✔ Both are used for state management in HTTP (stateless protocol)
🧠 8. Why Needed?
👉 HTTP is stateless, meaning it does not remember users.
✔ Cookies and Sessions solve this problem.
❓ 9. Likely Exam Questions
Short Questions
- What are cookies?
- Define session.
- Difference between cookies and sessions.
- What is session ID?
- What is the use of cookies?
Long Questions
- Explain cookies with example.
- Explain sessions with example.
- Compare cookies and sessions in detail.
- How do cookies and sessions manage state in web applications?
- Discuss advantages and disadvantages of cookies and sessions.
📝 10. Summary / Quick Revision
- Cookies = stored in browser
- Sessions = stored on server
- Used for state management
- Cookies: faster but less secure
- Sessions: secure but use server resources
👉 Both are essential for login systems, user tracking, and personalization in web applications.