Spiral model is same as the incremental model with more significant located on the risk analysis. Generally spiral model is distributed in four phases as- Planning, Risk Analysis, Engineering & Evaluation. In the spiral model any software project frequently moves throughout mainly these phases in the repetitions. This process is also known as the ‘Spiral Model’. Spiral model is begin from the ‘Planning’ stage or phase where requirements are gathering and the risk is appraised.   

Please see the below diagram related with the different phases of spiral model --

Here i am describing in short these four phases of spiral model as mentioned below --

• Planning Phase
• Risk analysis Phase
• Engineering Phase
• Evaluation Phase

Planning Phase:- In this phase we collected the requirements or information. These requirements are like business requirements or brs and system requirements or srs .  

Risk Analysis Phase:- Under this phase, a method is initiated to distinguish risk and alternative results. At the end of risk analysis phase we created a prototype.

Engineering Phase:- In the engineering phase we developed the application and performed testing. Means that development and testing both activities are performed in this phase.

Evaluation Phase:- Evaluation phase permits to the client or consumer to evaluate the outcomes of the application or project till project moves to the next spiral.

Advantages Of Spiral Model:- There are several types of advantages when using spiral model. Few advantages are mentioned as below --

• This model is good for the huge and important tasks projects.
• Powerful sanction and evidence manage easily.
• Product or application is created early in the software or application life cycle.
• In this model risk analysis activity is performed in large amount so shirking of risk is improved.

Disadvantages Of Spiral Model:- There are also many disadvantage of the spiral model. Few of them are mentioned as below --

• This model does not work for the small scale projects.
• This model is very expensive model to utilize.
• For the risk analysis needs extremely definite proficiency.

When we have to utilize the spiral model ? These areas mentioned as below --

• We can use this model when costs and risks estimation is significant.
• When consumers are uncertain of their requirements.
• When  requirements are complicated.
• Important modifications are only allowed.