THambrecht
That is the difference between MAC and PC. Pc is .aif and MAC is .aiff
It's the same file.
There is no 3 character limit to file extensions on the PC and hasn't been for some time.
Looking over my PC files I see both .aif and .aiff in the Live and Max folders as well as in many sample folders.
But, like WAV files, these are containers of chunks of data with each chunk having a data type.
One could make difficult to play versions of each. For example, only Sonar and Sound Forge (among the apps I have) will load and play 64-bit WAV files, and I imagine it may be easy for Apple audio apps to make files in AIFF that would be hard for most PC apps to play. And, while Sound Forge can read 64-bit files, it won't save them.