1. Go to your system profiler.
2. Click on the Mac icon in the top left hand corner of your screen.
3. Click on "About This Mac" then click on "more info".
4. Click on 'Software' on the left hand side. The information to the right hand side should say "yes" or "no" next to the 64-bit Kernel Extensions: text
Now, even if you are booting in 64-bit Logic may still be running in 32-bit mode. You can change this by Right-clicking (or Command (Apple) + I) the Logic program (from the finder window, not the dock) to get the information window open. There is a check box that says 32-bit mode... unclick this. The next time you boot Logic it will be in 64 bit mode. Watch it fly!
While most plug-ins that are 32-bit only will use a bridge and still function in a 64-bit environment, not all plug-ins may be compatible with Logic in 64 bit.
32 Bit users, how do you boot into 64 bit mode?
You can either hold down 6 and 4 every time you boot your Mac, or you can edit the terminal program. There is more information on this on the Apple website (click here).
The main advantage of using 64 bit mode is that you can address more then 4GB of memory, which is the limit on the 32 bit systems. This means that you can run much more CPU intensive plug-ins before getting errors in Logic!