noun
external storage device
Technical computing term for hardware that stores data outside the computer's main memory, such as hard disks, SSDs, USB drives, and optical discs.
外部記憶装置として外付けハードディスクを使っています。
I use an external hard disk as an external storage device.
Compound of 外部 (external) + 記憶 (storage/memory) + 装置 (device). A straightforward technical term with no special historical derivation.