Hola

im not understanding this term saying that the passport should be formatted for mac…i thought a harddisk can be used in mac and windows…

Normally Windows hard drives use the NTFS format and Macs use the HFS+, they are not compatible. If you use the FAT32 (limited to a maximum of 4gb per file) or the exFAT to format the hard drive, it will work on both OS.