The HDD vs. SSD choice comes down to a real mechanical difference, not just a price tier — and that difference explains both the price gap and where each still makes sense.
The mechanical difference
A hard disk drive (HDD) stores data on a spinning magnetic platter, read and written by a physically moving arm — the same basic mechanism hard drives have used for decades. A solid-state drive (SSD) stores data in flash memory chips with no moving parts at all, similar in principle to the memory in a smartphone or USB stick.
What that difference actually means
SSDs are significantly faster for both everyday file transfers and especially for tasks involving many small files, since there's no physical arm needing to move to different locations on a spinning disk. They're also more durable for portable use — no moving parts means far less risk of damage from being dropped or jostled while in transit, which matters a lot for something that's meant to be carried around. The tradeoff is cost: SSDs are still meaningfully more expensive per gigabyte than HDDs, though that gap has narrowed over time.
Where a cheaper HDD still makes sense
For large-capacity, infrequently accessed backup storage — an archive of old photos, completed projects, or a full system backup that mostly sits untouched — an HDD's lower cost per gigabyte is a genuine advantage, and the speed difference matters much less for something you're not actively working from day to day. For a drive that travels with you or that you're actively reading from and writing to regularly, an SSD's speed and durability advantages are worth the higher price.
Connection type affects real-world speed too
Even a fast SSD is bottlenecked by a slow connection — an SSD connected via an older USB standard won't come close to its actual read/write speed potential, since the connection itself becomes the limiting factor rather than the drive. Checking that both the drive and the port you'll actually use support a fast enough connection standard matters as much as the drive's own rated speed.
The one thing people forget
An external drive, of either type, is not a substitute for a real backup strategy on its own — it's one copy, in one location, subject to failure, loss, theft, or damage like any single storage device. Following the same "more than one copy, more than one location" principle that applies to cloud backup is worth applying here too, rather than treating a single external drive as a complete backup solution by itself.