在Win7/Mac OS X/Ubuntu文件系统中，可以保存在单个文件夹中的最大文件数是多少?

I'm wondering about what is the maximum number of files that can be present in a single folder, in the file systems used by all the prevalent OSes mentioned. I need this information in order to decide the lowest common denominator, so that the folder I'm building can be opened and accessed in any OS.I'm wondering about what is the maximum number