The spiral model was proposed by Bohem.
In spiral model the radial dimension represents the cumulative cost incurred in finishing the steps so far and angular dimension represents the progress made in completing each cycle of the spiral.
In the first quadrant of the spiral model each cycle begins with the identification of objectives for that cycle, the alternatives possible for achieving objectives and the constraints.
The next step is to evaluate these different alternatives based on objectives and constraints. The evaluation in this step is based on the risk perception of the project.
The next step is to develop strategies that resolve the risks, this step involves activities like bench marking, simulation etc.
After this the software is developed keeping in mind the risks and finally next stages are planned.