If
16 megabites RAM
and you meant 16 gigabytes, and
the file size is 3.6 megabites
and you also meant 3.6 gigabytes, then your just-for-fun model is pushing the limits.
The way AC controls geometry is not as efficient as it could be, and there are a very finite number of polygons, elements, SEOs, etc. that it can handle. Throw in everything else: floor plans, dimensions, elevations, sections, etc. that it needs to keep track of and your file size will increase significantly quite fast.
I remember there was a high rise project GS flashed to compete with Revit. I remember reading that the project had to be split in quite a number of module files to be workable. The master file was about 450mb and took 20 minutes to open, just to have the complete model. To open the 3D window took some more time as well.
450mb is not that big in terms of size, but I can only imagine the amount of information: if that's the size of only the master file without annotations, dimensions, elevations, sections, layouts, etc.; just to check the complete 3D model, imagine the information from all the other module files!
Every system has its limitations, and while AC will handle big projects quite well, there is always a roof. At least in 3D for any app, we'll just have to wait to what comes out of euclideon.com (if ever, unlimited detail FTW!!!) and then some more time to see it implemented.
On the other hand, AC offers a lot of flexibility when it comes to big projects... even more than in other systems.
Here are a couple of good reads. First one is quite old:
http://download.graphisoft.com/ftp/pdf/CreatingDatabases_Final.pdf
This one is newer.
http://www.archicadwiki.com/Big%20Building%20Whitepaper
The last one might give you a good idea of model size and AC limits.
Anyway, I know you are just playing around. In reality... I always try to keep everything as efficient as possible. The user experience with an efficient model vs. a slow one is quite different.
Best regards.
