iPod shuffles are designed to work on both Macs and PCs without special formatting. They are actually formatted using the Windows FAT32 file system, but, since Macs can read disks formatted like this, there is no need to reformat it. If you’re having a problem getting it to show up on your Mac when it’s connected, you need to restore it to factory settings. Launch the iPod Software Updater – if you don’t have this, you can download it here – connect your iPod shuffle, then click the Restore button to erase the iPod and reset it. You’ll lose its contents (data and music), so make sure you have them backed up.