Apple has released updates for Logic Pro and MainStage, allowing the applications to run in 64-bit mode. The main advantage of 64-bit support is that you can address vast amounts of memory.
With 64-bit mode, the application memory is not limited to 4GB as with 32-bit applications, so there is essentially no practical limit by today’s standards. As a result, all the installed memory that is not needed by the OS is available for use by Logic Pro or MainStage, which can be meaningful if your Mac has more than 4GB of memory installed. This larger amount of memory allows you to run far more instances of memory intensive plug-ins, such as sample-based software instruments.
Here Apple’s answers to some common questions about running in 64-bit mode:
Do Logic Pro or MainStage perform better in 64-bit mode?
In most cases there are only nominal performance improvements when running in 64-bit mode, other than the ability to run more instances of third-party memory intensive plug-ins. However, since Mac OS X v10.6 Snow Leopard is highly optimized for 64-bit operation, there may be some performance gains in areas where Logic interacts with it.
Can I use my existing Audio Unit (AU) plug-ins in 64-bit mode?
To make the transition to 64-bit easier, both Logic Pro and MainStage are still able to access 32-bit-only Audio Unit plug-ins while in 64-bit mode by using a utility application called 32-bit Audio Unit Bridge. This application opens automatically whenever a 32-bit-only Audio Unit plug-in is accessed. The 32-bit Audio Unit Bridge hosts all currently used 32-bit-only Audio Unit plug-ins and runs alongside Logic Pro or MainStage to provide access to the plug-ins being used.
The 32-bit Audio Unit Bridge has the same 4GB memory address limit as any other 32-bit application. Also, it is only possible to display and edit one 32-bit plug-in at a time.
Audio Unit plug-ins which are 32-bit only will appear in the channel strip plug-in insert menu under “Audio Units (32-bit)”. Audio Unit plug-ins which are 64-bit will appear in the normal location in the menu. Check with your favorite third-party plug-in developers for updated information on the availability of 64-bit versions of their plug-ins.
Is there a performance penalty when using the 32-Bit Audio Unit Bridge?
32-bit Audio Bridge does use some of your computer’s resources, but it is designed to operate extremely efficiently. In most cases, you should not notice any performance difference as compared to running the same plug-ins directly with Logic in 32-bit mode.
Note: While most 32-bit plug-ins should work with the 32-bit Audio Unit Bridge solution, not all plug-ins may be compatible.