Spiral model is used for high risky projects. here we make a part, verify that, then do enhancements and again verify and so on upto completion of project.
Spiral model is developed in recognition of the fact that systems development projects tend to repeat the stages of analysis, design and code as part of the prototyping process. Spiral model includes best features of both the classic Waterfall SDLC and the Prototyping approach.
What is usage of spiral model?