The original plan-driven SDLC: sequential phases (requirements → design → implementation → verification → maintenance), each fully completed before the next begins. Strong if requirements are fixed; brittle if they aren’t.
Key facts
Requirements frozen at the start.
Phase-by-phase, no overlap.
Heavyweight up-front planning ⇒ accurate budgets if everything else holds.
Painful to accommodate change late.
Traditional approach used for over 40 years.
Requirements must be defined at the start.
Little / no alternations.
Sequential - Complete 1 task and then the next.
Used in large scale SW development where thorough planning and predictability is required.
Pros
Extensive planning, this thoroughness often results in more accurate timelines and budgets.
Cons
Difficult to apply changes or modify / correct previous steps