When comparing back-up hard drives, some criteria to consider include each hard drive's type, speed, connectivity and amount of storage space. Back-up drives are typically external hard drives with some degree of portability. These include universal serial bus flash drives, disk-based hard drives and solid-state hard drives, as of 2015.
USB flash drives provide the most portability and don't require additional software or power sources. These allow for fast data transfer, but storage space is limited compared to other options.
Disk-based devices generally provide greater storage space at a more affordable price. Drives with 3.5-inch storage disks typically require an external power source, making them the least portable option. Drives with 2.5-inch disks generally draw power from the data connection, so they're more portable but have less storage capacity. Disk-based drives are typically slower than alternatives. Disk-based drives with higher rotations-per-minute ratings provide faster access to data.
Solid-state drives are more portable than disk-based drives and provide faster access to data due to their lack of moving parts. They also typically provide more storage space than USB flash drives. They're generally the most costly hard drive options available.
Disk-based and solid-state drives can connect to computers through a variety of connection standards, depending on the model. Connection options include USB 2.0 and 3.0, Ethernet cables, FireWire and wireless connectivity through a network. Faster options, such as USB 3.1 and Apple’s Thunderbolt, are available on some models, but consumers should check their computers for compatibility with these connector types.