It's early days so there are some graphical glitches here and there in this video (since fixed). This is a pre-release alpha of FL Studio 64 Bit in testing:
FL Studio works under 64 Bit Windows and can already host 64 Bit plugins. In addition by using 'Keep on disk' with Audio Clips/Sampler Channels AND OR 'bridging' 32 Bit plugins you can have access to unlimited memory/sample size and fill your RAM to overflowing, no matter how much you have, using in FL Studio 10 or higher.
See - http://www.image-line.com/support/FLHelp/html/panel_cpu.htm#Jump_memorymanagement
This development relates to the core FL Studio application and how it handles memory. It means FL Studio itself can access up to 192 GB of RAM under Windows.
See - http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx
It also means 32 Bit plugins will require bridging, this is the same for all 64 Bit software, just as 64 Bit plugins require bridging now under the 32 Bit software.
Finally, the tangible benefits of 64 Bit has little to do with Audio Quality or processing speed (marketing departments have vastly overstated its benefits here).
Background reading - http://www.soundonsound.com/sos/nov10/articles/64-bit.htm
for all your functional and musical questions
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