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There are many reasons why an external hard drive might not be recognized by your Mac – from incorrect formatting to a lack of power or a software problem.
External hard drive not recognized by Mac: Connect and visually inspect
Connect your external hard drive to your Mac using a USB cable:
- Normally, the hard drive should appear in the Finder under “Places” (formerly “Devices”).
- If it does not appear there, open Disk Utility via Finder under Applications > Utilities > Disk Utility.
- Check whether the hard drive appears in the left column.
- If the hard drive is displayed, right-click on it and select Mount (instead of Open Disk).
- If it is disabled, you can enable it this way.
Mac: Checking the format of the external hard drive
If the hard drive is recognized but cannot be opened, the file system format may be incompatible:
- Connect the hard drive to a Windows PC and check under “This PC” or “Computer.” Right-click > “Properties” to find the format. Possible formats:
- NTFS: Read-only by default in macOS, cannot be written to. For full write access, you need third-party software such as Paragon NTFS, Tuxera NTFS, or Mounty for NTFS (free, limited).
- FAT32: Compatible with macOS and Windows, but only suitable for files up to 4 GB.
- exFAT: The modern standard for cross-platform use (Windows/macOS). Please note: Older macOS versions prior to 10.6.5 require an update to recognize exFAT.
- If you want to change the format, first back up all your data – formatting will delete all content.
Check the power supply and hardware
If the hard drive is not displayed in Disk Utility, check the power supply:
Check hard drive for errors
If your hard drive is recognized but cannot be opened or behaves unusually, there may be an error in the file system. In such cases, an integrated macOS tool can help:
- Open Disk Utility and select the external hard drive.
- Click First Aid to check the hard drive for errors and repair them if possible.
Last resort: SMC and NVRAM reset
If all of the previous steps do not help, reset the SMC (System Management Controller) and NVRAM. These memory areas manage hardware functions such as USB connections.
- To reset the SMC (on Macs with Intel processors), shut down your Mac. Simultaneously hold down Shift + Control + Option on the left side and the power button for 10 seconds. Then release all keys and start the Mac normally.
- To perform an NVRAM reset, also turn off the Mac. Then start it up and immediately hold down Command (⌘) + Option + P + R. Hold the keys down for about 20 seconds, then release them.
