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Mac OS X 10.6 Snow Leopard: 32-bit vs. 64-bit
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Mac OS X 10.6 Snow Leopard: 32-bit vs. 64-bit

Q: Why are there separate listing for Mac OS X 10.6 32-bit and 64-bit on the drivers/updates page?
A: These listings are for the 32 & 64-bit kernel modes available with OS X 10.6 Snow Leopard. 
Mac OS X v10.6 Snow Leopard includes a 64-bit kernel.  On hardware that supports the 64-bit kernel, you can choose whether to start up (boot) your Mac using the new 64-bit kernel or the earlier 32-bit kernel, and some of the newest Mac’s start up using the 64-bit kernel by default. M-Audio provides universal kernel extensions which contain the code for 32-bit Intel, 64-bit Intel, and Power PC (PPC) systems. 
Q: How can I tell whether I’m running a 32-bit or 64-bit kernel?
A: Use the System Profiler to determine if you're running a 64-bit kernel. From the Apple menu, choose About this Mac, then click More Info. In the Contents pane, select Software. If 64-bit Kernel and Extensions is set to Yes, you are running a 64-bit kernel; if set to No, you are running a 32-bit kernel.
Q: What about 64-bit applications? Are M-Audio drivers compatible with 64-bit applications?
A: Device drivers, such as those for Fast Track USB or ProFire 2626, run in the Kernel and do not directly communicate with applications. When posted on the M-Audio drivers/updates page for a 64-bit version of Mac OS X 10.6, the driver will have a kernel extension compatible with the 64-bit kernel. Refer to your software manufacturer to determine if your software is compatible with the 64-bit kernel.
When running a 32-bit kernel it is still possible to run applications in a 64-bit mode, like Logic Pro (9.1 and above) and Cubase 6, on systems with 64-bit processors. This means that 64-bit applications are able to use more than 4GB of RAM, even when running a 32-bit kernel. Since M-Audio drivers do not communicate directly with applications, changes to the driver are not required for applications that support a 64-bit mode.
Software such as VST plug-ins, and add-ons like HyperControl and DirectLink, do communicate directly with the application and therefore must be updated to be compatible with software that runs in a 64-bit mode. Check the Release Notes section of the download page for notes about compatibility with an application in 64-bit mode.
Q: Does running a 64-bit kernel have an impact on applications I usually run?
A: No, but it can have a significant impact on kernel extensions, usually used to enable third-party product hardware and special features. 32-bit kernel extensions will not work when your computer is running a 64-bit kernel. Products that use 32-bit kernel extensions may not work or may not recognize their associated hardware.