Storage has never been more plentiful or less expensive. For as little as $50, you can add a terabyte (TB) to your laptop or desktop via an external drive. That's enough to house hundreds of movie files or hundreds of thousands of MP3s or photos. Every computer you can buy, from huge desktop towers to budget-price Windows tablets, can connect to at least one hard drive, with no complex installation required. And if you're lucky enough to have multiple I/O ports, you can hook up many more. But which to choose? Here's everything you need to consider when shopping for an external hard drive.
Hard Drive Types
There are two types of external drives. Desktop-class drives, with 3.5-inch mechanisms inside, require a power adapter. They are designed to stay in one place, typically on your desk at home or at the office. If you're buying a desktop-class drive for video or lots of file transfers, look for one with a built-in fan, as the extra cooling will extend the drive's life expectancy. Notebook-class (aka pocket or portable) hard drives are usually 2.5-inch mechanisms powered through the connector cable. You can slip a 2.5-inch model into a coat and even some pants pockets.
Desktop-class models currently top out at 8TB per mechanism, but some drive manufacturers put two or more mechanisms into a chassis for more storage (for example, two 4TB drives for a total of 8TB of storage). Notebook-class drives come in capacities up to 4TB, but capacities from 500GB to 2TB are most common.
A word about multiple drives: You can increase capacity, speed, or data protection by buying an external RAID array, but multiple drives add expense and (some) complexity. Once you connect a single-volume external RAID array to your PC or Mac, it will show up and act as any other external drive. After that, it can become more complex. You should consider a drive with support for RAID levels 1, 5, or 10 if you're storing really important data that you can't afford to lose. There are other RAID levels for speed and capacity, and both software and hardware RAID implementations. Read our primer, RAID Levels Explained, for a more in-depth explanation.
Another type of external storage is the solid-state drive (or SSD), which uses a type of flash memory to store data rather than spinning platters. These drives are faster, and in most cases cost quite a bit more than external hard drives. Check out The Best SSDs for our recommendations. Want to know more about how hard drives and SSDs compare? Check out SSD vs. HDD: What's the Difference?
Input, Need Input
External drives connect to PCs and Macs via external cables. USB 2.0 and 3.0 ports are almost always present, though there are also newer connectors like USB-C. USB 3.0 provides fast transfer speeds (up to 5Gbps theoretical throughput) and a minimum of fuss, since it's backward-compatible and almost all desktop and laptop PCs come with USB ports. The newer USB-C standard is faster still (10Gbps, or twice the speed of USB 3.0) and supported using the smaller and more convenient USB-C connector, but right now it is still somewhat uncommon to find on drives.
You may find older external SATA (eSATA) or FireWire ports on some drives, though they can't reach the speeds that USB 3.0 or USB-C can. Thunderbolt and Thunderbolt 2 use the Mini DisplayPort connector and promise even faster speeds (up to 20Gbps), but have largely been supplanted by USB-C ports with Thunderbolt 3, which boast blazing throughput of 40Gbps (assuming your computer supports the technology). Although Thunderbolt, which was originally developed by Intel and championed by Apple, has been something of a niche player, the inclusion of only USB-C/Thunderbolt 3 ports on Apple's new MacBook Pro laptops could easily spur wider-spread adoption within the coming year.
The external drives we've reviewed all have USB connectivity of one sort or another, but it's important to check that the drive you're considering is compatible with your computer. A handful of USB memory sticks and hard drives are currently available with both USB 3.0 and USB-C support via two separate connectors. Optional adapters will let you use older USB drives with PCs with newer USB-C ports.
How Important Is Drive Speed?
While a 7,200rpm drive is inherently faster than a 5,400rpm drive, the real answer would be "it depends." If you are transferring lots of files over a speedy interface like USB 3.0/USB-C or Thunderbolt, then by all means go for the 7,200rpm drive. But if you're limited to USB 2.0 or FireWire, then I would trade speed for capacity and get the largest 5,400rpm drive your budget allows. USB 2.0 and FireWire 800 are older interfaces that work fine with a 5,400rpm drive. If all-out speed is your goal, running multiple drives over Thunderbolt 3 is the fastest (and costliest) way, with a single SSD connected via Thunderbolt 1/2 or USB 3.0/3.1 as next fastest, and so on.
Other Factors
Do you care what your drive looks like? You can buy different colored drives for each family member, for example. Included software is a factor if you don't already have a local or online backup plan. If you're simply using the drive as an extra storage container, or if you're using the backup software built into Windows or macOS, the software bundled with the drive isn't as important. Warranty length is also a big factor in our ratings: Drives can and will fail. That cheap drive you found on a deal site may only come with a one-year warranty. Look for a three- or five-year warranty if you're hard on your drives.
To get you started toward the right add-on backup/storage solution, below are 10 of the best drives we've tested. For more options, take a look at our lists of the best network-attached storage (NAS) drives and cloud storage services.