SD cards under 32Gb in size use FAT32. Larger cards require ExFAT. The S4 recognizes both file systems.
Mac OS X Snow Leopard starting from 10.6.5, Mac OS X Lion and OS X Mountain Lion work with ExFAT. On the Windows side Windows Vista SP1 and later desktop operating systems include the exFAT file system. There is an Upgrade patch for Windows XP.