Know and understand characteristics, uses, advantages and disadvantages of the four methods of implementation, direct changeover, parallel running, pilot running, phased implementation

The Systems Life Cycle – Implementation Phase

After a system has been designed, built, tested and approved, it must be introduced into the organisation. Four main methods are used to move from the old system to the new one.

1. Direct Changeover (Big‑Bang)

This method switches off the old system and switches on the new system at a single point in time.

• Characteristics: Immediate, all‑or‑nothing transition.
• Typical Uses: Small organisations, low‑risk systems, or when the old system is no longer functional.
• Advantages

  • Fast implementation – no period of dual operation.
  • Low cost – no need to maintain two systems simultaneously.
  • Clear cut‑over point simplifies planning.

• Disadvantages

  • High risk – any failure leaves the organisation without a working system.
  • Little opportunity to correct problems after go‑live.
  • Staff may be unprepared for sudden change.

2. Parallel Running

Both the old and the new systems operate simultaneously for a defined period.

• Characteristics: Redundant operation; data is entered into both systems.
• Typical Uses: Critical systems (e.g., payroll, finance), high‑risk environments.
• Advantages

  • Safety net – if the new system fails, the old system continues to operate.
  • Allows thorough testing with real data.
  • Provides time for staff training.

• Disadvantages

  • Increased cost – two systems must be maintained.
  • Potential for data entry errors and inconsistencies.
  • Longer implementation period.

3. Pilot Running (Trial Implementation)

The new system is introduced to a limited area, department or group before full roll‑out.

• Characteristics: Controlled trial; feedback is used to refine the system.
• Typical Uses: Large organisations, systems with varied user requirements, or when the impact is uncertain.
• Advantages

  • Identifies problems early in a low‑risk environment.
  • Allows customisation based on real user feedback.
  • Reduces overall disruption to the organisation.

• Disadvantages

  • May delay full benefits until the pilot is completed.
  • Requires careful selection of the pilot group to be representative.
  • Potential for “pilot‑itis” – endless tweaking before wider release.

4. Phased Implementation (Staged Roll‑out)

The new system is introduced in stages, either by function (e.g., accounting first) or by geography (e.g., one branch at a time).

• Characteristics: Incremental deployment; each phase builds on the previous one.
• Typical Uses: Large, complex systems; organisations with multiple sites or departments.
• Advantages

  • Spreads cost and resource demand over time.
  • Allows users to adapt gradually.
  • Problems can be isolated to a specific phase.

• Disadvantages

  • Longer overall implementation period.
  • Requires careful integration between old and new modules during overlap.
  • Potential for inconsistency if phases are not well coordinated.

Comparison of Implementation Methods