WD 1TB Black My Passport Ultra Portable External Hard Drive - USB 3.0 - WDBGPU0010BBK-NESN [Old Model] 4-inch Form Factor, 1TB Storage Capacity Formatted NTFS for Windows 8.1 or Windows 7 operating systems. Requires reformatting for Mac OS X operating systems. Compatibility may vary depending on users hardware configuration and operating system. USB 3.0, Password Protection with Hardware Encryption WD Backup, Option to backup to Dropbox using cloud services, Includes Quick Install guide and USB Cable 3-year limited warranty Formatted for Windows. For Mac compatibility this Hard Drive requires reformatting. Refer to Application Guide for guidance on this