1960s – first significant model developed – Standard Development Life Cycle (SDLC), also known as waterfall method. Splits software development process into stages:
Model has high level of abstraction – seven stages. No models have lower abstraction guiding development process.
Has Systems Thinking approach – Maintenance loops back into Requirements – software development is circular/iterative process with inputs, outputs, controls and feedback.
V-model and W-model followed on, emphasis on quality and testing.