Incremental life cycle model.

B'coz,
Generates software quickly.
More flexible and less cost to chane of requirements.
Easy to test and debug during iteration.
Easy to manage the risk.

1.Spiral model is called a meta model.Spiral model is made 
with the features of Prototype model and Waterfall model.
2.Spiral model takes special care about Risk Analysis. 
Whreas it is not given importance in Prototype model.

Microsoft company made office hindi software.

ramdayal microsoft company

Wired to Deliver

Requirement Analysis 
High level design
low level design 
construction & unit testing
system and integration testing
Acceptance 
maintance

Software development life cycle consists of four phases.
That is,
1.Analysis
2.Design
3.Implementation and
4.Testing

1.Analysis: Define the goals.Gathering the requirements to 
develope a software for customer satisfaction.Aanalyse that 
how to use and design?.

2.Design: Detailed design the requirements as a structure.

3.Implementation: Implement the detailed design with 
designed code.

4.Testing: Check the whether the software will work 
properly or satisfies the customer expectation.
If it is satisfies the customer needs, that software 
properly produced.

This is software development life cycle.