The Basic COCOMO Model estimates the effort required to develop software in three modes of development (Organic Mode, Semidetached Mode, or Embedded Mode) using only DSIs as an input. The Basic model is good for quick estimates.
The Intermediate Model extends the Basic Model with an Effort Adjustment Factor (EAF) and different coefficients for the effort equation. The user supplies settings for cost drivers that determine the effort and duration of the software projects. It also allows DSI values and cost drivers to be chosen for individual components instead of for the system as a whole.
The Detailed COCOMO Model uses effort multipliers for each phase of the project and provides a three-level product hierarchy and has some other capabilities such as a procedure for adjusting the phase distribution of the development schedule.
["Software Engineering Economics", B. Boehm, Prentice-Hall, 1981].