External hard drives, ranked by cost per terabyte

An external hard drive is a 2.5-inch or 3.5-inch HDD packaged in an enclosure with a USB (or occasionally Thunderbolt) interface, ready to use the moment you plug it in. No mounting, no cables inside the case, no driver setup — which is exactly why they remain the most popular backup and overflow-storage device for laptops and desktops alike. Large desktop models that include their own power adapter reach the highest capacities and the best cost per terabyte; bus-powered portable models trade some capacity and value for the convenience of running off a single cable.

When comparing value, look past the headline price to the $/TB, and note the form factor: desktop 3.5-inch units almost always beat portable 2.5-inch drives per terabyte. Interface speed (USB 3.2 Gen 1 vs Gen 2) matters for transfer time but not for capacity value. One quirk worth knowing: large external desktop drives are frequently cheaper per terabyte than the equivalent bare internal drive, because manufacturers price the finished consumer product aggressively. Enthusiasts ‘shuck’ these enclosures to recover a high-capacity internal disk — a real way to lower your $/TB if you accept the warranty trade-offs.

Desktop vs portable, and the case for shucking

External drives split into two families. Desktop units use 3.5-inch drives and a wall adapter; portable units use 2.5-inch drives and draw power from the USB port. The difference in capacity and $/TB is large.

‘Shucking’ means removing the internal drive from a desktop enclosure to use it bare. It can meaningfully cut your $/TB, but voids the enclosure warranty and occasionally yields a drive with non-standard power pins. If you only need plug-and-play backup, leave it sealed. For a deeper look at backup planning, see our backup strategy guide.