In the beginning...

... there was the stylus.

And it was good.

The stylus evolved by small steps into the pencil, and, later, the pen. With these tools architects and engineers plied their trades for generation upon generation, drafting on paper, parchment, vellum and mylar. But there were limits. Hand drafting took a great deal of time, high quality reproductions were difficult to produce and stacks of paper and trace piled higher and higher.

Then came CADD.

Computer Aided Drafting and Design brought the AEC field into the computer age, promising faster, more reproducible work which could be produced in less time. CADD slowly grew to include three dimensional computer models and renderings. But there were limits. For all it's sophistication, it could easily be fudged, it wasn't very smart and proper three dimensional modeling for spatial coordination was time consuming and not very effective.

Now there is BIM.

Building Information Modeling has taken CADD to the next level. Instead of drawing lines that represent walls, you select a wall tool and in one quick stroke model the wall in three dimensions, with built in information such as layers of gypsum wallboard, brick, air spaces, structural support type, fire ratings, acoustical qualities, wall types and many more. Coordination within a project discipline has been brought to a new level, which coordination between disciplines going even farther when models are linked. Many modeling programs, such as Revit, can even be linked with software designed for specification writing. BIM has its limits, but right now, it is the leading edge in the AEC world.