have machines running 64bit Win7 + 64bit ACAD  -However they are only using 2gb of the available 6gbOpening large files (around 9-10gb) results in 'Autocad -not responding'   - however -after long delay -will open- but be so slow as to be unusable.(eg - 10 or 20 min to open -or respond to any change of tab change etc).Window's resource manager clearly shows only 2gb being used -also shown as ' around 30% total memory use'.I'ts also clear that drawings grind to a halt -as they approach 'using up' this 2gb limit.(other software will quite happily take advantage of the avaiable memory above this 'limit')Its as though ACAD is in 32 bit mode - i.e. not aware of the memory above the 2gb level.Anyone any ideas ? Not getting far with our 'paid for' autodesk support so far !

This may be a silly question but do you have a really good video card installed in this machine as well? You need alot of RAM and a good graphics card to get a good result, just a thought, I am no expert but I lock up my CAD all the time and it is because I do not have a machine that handles it well enough on larger files. Usually the RAM runs out on me. But I also know I needed and good VGA card....just a thought, again, no expert...