CSS CS Optional — Paper-I, Section-B, Topic V.

🔑 System Delivery

• Deployment planning: staged rollout vs "big bang"
• Data migration from old system
• User training
• Documentation handover
• ⚠️ No rollback plan → minor bug becomes an outage.

📌 Maintenance — 4 Types (memorize verbatim)

• Corrective — fix bugs found after release.
• Adaptive — adjust to changed environment (new OS/hardware/regulation).
• Perfective — improve performance / add requested features.
• Preventive — refactor/re-engineer before problems occur.

📌 Why Maintenance Is Most Expensive SDLC Phase (60–80% of lifetime cost)

• Longest duration (years/decades)
• Accumulated complexity ("software entropy"/"code rot")
• Lost context (original devs move on)
• Regression risk (every change needs re-testing)

🔥 Past Papers

• 2026 Q6(a) — why is maintenance the most expensive phase? (name all 4 types)

⚠️ MCQ Trap