Opposite branch of tashkent university of information technologies named muhammad al-khorazmi

Iterative Model
The iterative development model develops a system by building small portions of all the features. This helps to meet the initial scope quickly and release it for feedback.
In the iterative model, you start off by implementing a small set of software requirements. These are then enhanced iteratively in the evolving versions until the system is completed. This process model starts with part of the software, which is then implemented and reviewed to identify further requirements.
Like the incremental model, the iterative model allows you to see the results at the early stages of development. This makes it easy to identify and fix any functional or design flaws. It also makes it easier to manage risk and change requirements.
The deadline and budget may change throughout the development process, especially for large complex projects. The iterative model is a good choice for large software that can be easily broken down into modules.

RAD Model
The Rapid Application Development (RAD model) is based on iterative development and prototyping with little planning involved. You develop functional modules in parallel for faster product delivery. It involves the following phases:

1. 
   Business modeling
   
2. 
   Data modeling
   
3. 
   Process modeling
   
4. 
   Application generation
   
5. 
   Testing and turnover
   

The RAD concept focuses on gathering requirements using focus groups and workshops, reusing software components, and informal communication.
The RAD model accommodates changing requirements, reduces development time, and increases the reusability of components. But it can be complex to manage. Therefore, the RAD model is great for systems that need to be produced in a short time and have known requirements.

Spiral Model
The spiral model is a risk driven iterative software process model. The spiral model delivers projects in loops. Unlike other process models, its steps aren’t activities but phases for addressing whatever problem has the greatest risk of causing a failure.
It was designed to include the best features from the waterfall and introduces risk-assessment.
You have the following phases for each cycle:

1. 
   Address the highest-risk problem and determine the objective and alternate solutions
   
2. 
   Evaluate the alternatives and identify the risks involved and possible solutions
   
3. 
   Develop a solution and verify if it’s acceptable
   
4. 
   Plan for the next cycle
   

You develop the concept in the first few cycles, and then it evolves into an implementation. Though this model is great for managing uncertainty, it can be difficult to have stable documentation. The spiral model can be used for projects with unclear needs or projects still in research and development.