External drives · Mounting and drive problems

Why does my external drive work on my old Mac but not my new one?

Short answer: Usually a setting or the connection: approve it under Allow accessories to connect on newer Mac laptops, try another adapter or cable, give it more power with a powered hub, and run First Aid if it's detected but won't mount.

Usually it's the connection or a setting rather than the drive. Check these, in order:

  1. Allow accessories — newer Mac laptops ask before a new accessory connects; if it was declined, the drive stays hidden. See Allow accessory to connect.
  2. Adapter and cable — a USB-A drive needs an adapter; cheap ones can be power- or data-limited. Try another.
  3. Power — new Mac ports or hubs may supply less than the drive needs; try a powered hub.
  4. Format — a drive formatted for very old systems still reads, but a damaged one may need First Aid.

If Disk Utility sees it but Finder doesn't, see mounting a drive.

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