One External Drive, Two Systems: Mac and Windows

Choosing the file system

Two candidates. NTFS for important data and large capacities, with a driver on the Mac. exFAT for quick small-file swaps. APFS and Mac OS Extended are invisible to Windows, so they are out.

Setting up the Mac side

On the NTFS route, install DiskBee and drives mount writable. Windows needs nothing at all, since NTFS is its native format.

Two habits to build

• Eject on the Mac, use Safely Remove on Windows, every single time. The write cache needs the warning.
• When Windows offers to scan and repair the drive, let it run once and continue.

Cross-platform details that catch people out

• Windows rejects these characters in file names (\ / : * ? " < > |), and files carrying them may not open there;
• files deleted on the Mac land in a hidden .Trashes folder and keep occupying space, so empty it from Windows now and then;
• turn off Fast Startup in Windows, or the NTFS partition can stay hibernation-locked and mount read-only on the Mac.