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How much capacity? For full-system backups of a computer with a 1 to 2TB internal SSD, a 1TB external storage drive should be adequate because imaging software such as Acronis uses a lot of compression.
The 20 and 40 Gbps speeds are nicer, but not worth it unless you are a creative professional. If you are getting an external SSD and your PC has at least one 10 Gbps port, we recommend spending a little extra to upgrade to 10 Gbps.
What USB connection? You can get a drive with a USB or Thunderbolt interface that operates at up to 5 Gbps (USB 3.x), 10 Gbps (USB 3.1 / 3.2 Gen 2), 20 Gbps (USB 3.2 Gen 2x2) or 40 Gbps (Thunderbolt or USB 4) but you'll pay more for the privilege. But if you need cavernous amounts of external storage, a hard drive is a better option for most, as multi-terabyte external SSDs sell for several hundred dollars, but 4TB portable hard drives can sell for under $100 (£90). A portable SSD will also be much faster at reading and writing lots of data. If you don’t need terabytes of storage and you often travel with your drive, a portable SSD is worth paying extra for.
But they’re also much slower and more fragile than solid-state drives. Portable Hard Drive or SSD? Drives that have spinning storage platters inside are very affordable, with 1TB models often selling for under $50 (£40).