By default, software will do not split the generated file. But if your Wii hard drive is FAT32 format, then your WBFS files cannot be larger than 4GB, in this case, you need choice the second option "Size: 4GB", then if the generated file will be larger then 4GB, it will be splitted to wbfs, wbf1, wbf2, wbf3, and etc.. If your Wii hard drive is in NTFS format, you do not need split the file.