Fat Client vs Fat Server
1. Where does the processing live?
In any client/server system the business logic and data management can be pushed either to the client or to the server. The extreme placements define:
- Fat (thick) client — most processing at the client; server only stores/serves data.
- Fat (thick) server — most processing at the server; client is a thin terminal/browser.
FAT CLIENT FAT SERVER
+---------------+ +---------------+
| presentation | | presentation | (thin: browser /
| business logic| network +---------------+ terminal)
| data access | <-=====-> | business logic|
+---------------+ | data access |
(client) +---------------+
only data moved (server)
2. Comparison
| Criterion | Fat Client | Fat Server |
|---|---|---|
| Processing load | Mostly at client | Mostly at server |
| Client type | Powerful PC/workstation with installed software | Dumb terminal, thin client, browser |
| Business logic location | Client side | Server side |
| Data access | Client queries and processes results (often full DB copy) | Server executes query and returns only result set |
| Network traffic | Low per operation (local processing) | High (every request/response round trip) |
| Software distribution | Hard — must install/update on every client | Easy — update once at server |
| Security | Weak — logic and data visible at client | Strong — logic and data centralised |
| Client hardware cost | High | Low |
| Server hardware cost | Low | High (powerful servers) |
| Maintenance | Expensive, version drift ("fat client chaos") | Cheap, centralised |
| Offline operation | Possible | Not possible (depends on server) |
| Example | Two-tier DB app with heavy client (classic VB/PowerBuilder) | Mainframe, thin web client, 3-tier JEE |
3. Thin Client / Thin Server Terminology
- Thin client — only the presentation layer (browser, terminal); zero administration client.
- Thin server — a server that only serves files/pages with no application logic (rare, a mis-design for dynamic systems).
- Most modern web systems are thin clients + fat (multi-tier) servers — the browser holds only HTML/CSS/JS; all business logic and data live in server tiers.
4. Choosing Between Them
| Situation | Preferred |
|---|---|
| Many low-power clients, fast changing logic, strict security | Fat server (thin client) |
| Occasional disconnection, heavy graphics/local computation | Fat client |
| LAN with light traffic, desktop-class users | Fat client acceptable |
| Internet with unknown bandwidth | Fat server (thin client) |
5. Exam Points
- Differentiate fat client and fat server with a diagram — 7 marks.
- Tabular comparison of fat client vs fat server (any 8 points) — 10 marks (frequent).
- What is a thin client? Why do modern web apps prefer thin clients? — 5 marks.