According to the New Oxford American Dictionary on my iMac, CAD is an abbreviation for Computer Aided Design. Wikipedia, Autodesk, Dictionary.com, webopedia, and many more all concur. In fact, if you do a quick google search for "CAD" you would be hard pressed to find a reference to anything related to Architecture that does not define CAD as Computer Aided Design.
I would argue, however, that the vast majority of CAD users use the computer and CAD software in the capacity Computer Aided Drafting. A much better definition of the term in my opinion. When i was first introduced to CAD back in 1994, it was more common to talk about it in terms of drafting rather than design. As it was just starting to make major headway into the industry and schools at the time, people may have had a different (more accurate?) perspective on what exactly it was. Now that it is a much more pervasive tool, we may have lost sight of the fact that it is a representational tool. The more common reference to "design" in CAD is indicative of this.
While there are some instances in which a computer software package may aid in the design of a building. Generally speaking it does not. It merely aids in the representation of the building design. It is substitutionary for a parallel bar / T-bar and triangles. The design happens elsewhere. It is hashed out and refined through representational iterations. But it does not happen in the representation, whether generated manually or with the aid of the computer.
But what is "drafting" then. As related to architecture, we understand it as representation of a building through technical drawing. Interestingly enough, the New Oxford American Dictionary defines 'draft' in terms of preparing a preliminary version (among other things). So drafting in architecture, is to prepare a preliminary version of a building through technical drawing. And this is really what one is doing when drawing a building utilizing a computer and any number of available software packages as a tool.
Often times Architects will work out designs through manual sketching. Getting many iterations of design ideas out quickly. Honing the design and then taking it into the computer for further refinement, more elaborate representation, or simply to produce construction documents.
As such, CAD can be used to produce 2D or 3D representations of the building. Modeling a building in the computer is a type of drafting. Which brings us to Building Information Modeling, known as BIM. Full disclosure, i am a novice in the world of BIM. Just starting to get into it, i can only really speak from my limited understanding of what it actually is. But as i understand it, BIM is a technology that allows us to model a building in the computer as though it is actually being constructed. In so doing, it allows for material take offs, better coordination between the various systems, and linking 2D drawings to the model so that updating the model updates all the drawings. This is likely an overly simplistic notion of BIM, but again, it is based on my limited understanding. Some have argued that, due to this increase of information contained in the model, BIM is no longer CAD. My knee jerk reaction to this is "yes, it is." As i delve further into the world of BIM, i may change my mind on this stance. But as defined above, BIM is still a form of drafting. Of preparing a preliminary version of a building. Because the model contains more information does not necessarily remove it from the scope of CAD.
So CAD is the use of a computer and software to make the representation of a building design more efficient, more effective, and more informative. It is amazing the lack of information you will see on an old set of blueprints as compared to what a set of drawings contain today. And with the continuing emergence of BIM in the production of drawings, i imagine the amount of information will only increase further. But that being said, drawing with a pencil on paper, replicating that method in a computer, or modeling a building in the computer are all still forms of drafting. The computer makes it more efficient and more accurate, but it does not fundamentally change the nature of what is produced.
P.S. CAD is not necessarily AutoCAD. There is a range of software packages out there that are utilized for various different reasons. While AutoCAD can (for now) claim to be "the industry standard," it is not the end all and be all of CAD solutions. In the next few posts, i will delve into my own history with CAD and talk about what software i currently use and why.