Spiral Model:

Spiral Model:

The spiral model is a realistic approach to the development of large-scale software products because the software evolves as the process progresses. In addition, the developer and the client better understand and react to risks at each evolutionary level.
The model uses prototyping as a risk reduction mechanism and allows for the development of prototypes at any stage of the evolutionary development.
It maintains a systematic stepwise approach, like the classic Life Cycle model, but incorporates it into an iterative framework that more reflect the real world.
If employed correctly, this model should reduce risks before they become problematic, as consideration of technical risks are considered at all stages

Spiral Model Strengths:

Provides early indication of insurmountable risks, without much cost
Users see the system early because of rapid prototyping tools
Critical high-risk functions are developed first
The design does not have to be perfect
Users can be closely tied to all life cycle steps
Early and frequent feedback from users
Cumulative costs assessed frequently

Spiral Model Weaknesses:

Time spent for evaluating risks too large for small or low-risk projects
Time spent planning, resetting objectives, doing risk analysis and prototyping may be excessive
The model is complex
Risk assessment expertise is required
Spiral may continue indefinitely
Developers must be reassigned during non-development phase activities
May be hard to define objective, verifiable milestones that indicate readiness to proceed through the next iteration