Audacity has no 64-bit version of it, but although it should run on 64-bit systems. Sufficient RAM must be available to run Audacity smoothly and support the greater memory requirements of 64-bit systems compared to 32-bit.
Windows and Linux. Sound device drivers specific to the 64-bit operating system are essential on 64-bit versions of Windows XP, Vista and 7, and on 64-bit Linux. If you upgrade it from a 32-bit to 64-bit operating system, you are required to have 64-bit capable computer, and you also should update the sound device drivers to a 64-bit version.
If you are upgrading from 32-bit Windows XP to 64-bit Windows Vista or 7 you should make especially sure that you computer supports Audacity's minimum system requirements for Windows.
Mac OS X. We strongly recommend you to use the Beta version of Audacity for 64-bit systems. OS X 10.5 supports both 64-bit and 32-bit processors equally well, with few if any issues with the supplied system drivers.