How do I connect a 2015 iMac to a iMac M4 for data migration using Thunderbolt or USB?

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Level 1

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How do I connect a 2015 iMac to a iMac M4 for data migration using Thunderbolt or USB?

I am trying to use Migration Assistant to move all data from wife's "old" Late 2015 iMac with Thunderbolt (ports 1 & 2) & USB 3 to her "New" 24" 2024 M-4 iMac with Thunderbolt 4 ports (and USB 4). Do I need a wire adapter? The wires I have don't seem to work/fit.

Migration says it if finished after about 20 hours with WiFi and same with the wires I have BUT the "new" desktop is empty as are the 4 "Apple" file folders on the "new" screen. Apple Care spent a long time with me, but I don't seem to be successful.

[Re-Titled by Moderator]

Original Title: USB wire adapter needed?

iMac 24″, macOS 26.1

Posted on Nov 28, 2025 8:32 AM

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Answer 1

Top-ranking reply

D.I. Johnson

Level 7

32,159 points

Nov 28, 2025 9:46 AM in response to Weckerling

Get hold of an external drive with at least 2x the storage capacity of the 2015 iMac and create a Time Machine backup.

Then connect that backup drive to the new iMac and migrate from that.

Back up your Mac with Time Machine - Apple Support

Transfer to a new Mac with Migration Assistant - Apple Support

When done, you can continue to use that external drive as a backup destination for Time Machine on the new Mac.

Backups are good, unless your data means nothing to you.

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Answer 2

Nov 28, 2025 10:01 AM in response to Weckerling

An HDD for Time Machine as was an excellent suggestion, or maybe a NAS if you have multiple Macs and want to share one pool of storage as a NAS. The NAS can be purpose-built commercial with Time Machine server capabilities such as Synology or Unifi UNAS, or can open-source using TrueNAS or ZimaNAS on some spare x86 or Arm hardware and storage, or an existing Mac with directly-connected storage.

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Answer 3

rkaufmann87

Level 10

148,440 points

Nov 28, 2025 2:26 PM in response to Weckerling

If you want to migrate please follow the simple instructions in Setup Assistant and Migration Assistant, this method works 100% of the time assuming 2 things:

Your Time Machine backup External Hard Disk is in good working condition.
You bought a new Mac with adequate storage space. Adequate storage space means that the new Mac has at least the same or more storage space as the old Mac.

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