Depending on the application, we recommend that you pay attention to the following characteristics when purchasing an external hard disk: If you are primarily looking for a portable hard disk or want to exchange data between different devices in an uncomplicated way, a 2.5'' hard disk with power supply via an integrated USB interface is a good choice. These smaller hard disks usually have a storage capacity of up to 5000GB. When selecting the connection, the speed differences are shown. Most manufacturers today rely on the fast USB 3.0 standard. Newer hard disks already have the universal USB Type-C connection. Individual models also have the option of exchanging data via WiFi. For home users who want to back up their documents and multimedia data such as holiday photos, we recommend external hard disks with a size of 3.5'' and a storage capacity between 500 and 5000GB. For Mac users, it is recommended to consider products with the fast Thunderbolt 3 connector. Backup systems with a storage capacity of 5000GB or more and a RAID function are suitable for companies or for backing up large amounts of data. Rack systems can also be considered for larger storage capacities. These offer storage capacities of up to 64 TB and can be installed in a space-saving manner.