The disk you inserted was not readable by this computer error

If you’ve ever connected an external hard drive, USB stick, or SD card to your Mac and received the message “The disk you inserted was not readable by this computer,” you know how frustrating it can be. This error means your computer is unable to properly recognize or access the storage device. The issue can arise for multiple reasons, ranging from simple formatting incompatibilities to more serious hardware damage. Understanding the causes and solutions can help you recover your data and restore normal functionality.

Common Causes of the Error

Unsupported File System

If the drive is formatted with a system that macOS doesn’t recognize (such as some Windows-specific file systems), your Mac may show this error.

Corrupted File System or Partition

Power failures, improper ejection, or malware can corrupt the drive’s file system, making it unreadable.

Damaged or Failing Drive

Physical issues such as bad sectors or worn-out hardware can cause the computer to reject the disk.

Connection Problems

Faulty USB cables, damaged ports, or insufficient power supply (especially for larger HDDs) can trigger the error.

Driver or OS Incompatibility

Outdated macOS versions may not properly support certain storage formats.

Troubleshooting and Fixes

1. Check the Connection

Start with the basics:

Try a different USB port or cable.

If it’s an external HDD that requires external power, confirm that the power adapter is working.

Test the drive on another computer to rule out issues with your Mac’s hardware.

2. Use Disk Utility

On macOS, open Disk Utility:

If the drive appears in the sidebar but is grayed out, you can attempt to run First Aid to repair the disk.

Sometimes, simply mounting the drive manually in Disk Utility resolves the issue.

3. Reformat the Drive

If repair fails and you don’t need the existing data, you can erase and reformat the disk:

Choose a file system format compatible with macOS, such as APFS or Mac OS Extended (Journaled).

For cross-platform use between Mac and Windows, select exFAT.

Be aware this will delete all data on the drive.

4. Recover Data Before Formatting

If you need the data, consider using data recovery software before erasing. Third-party tools can often retrieve files from corrupted or unreadable drives.

5. Check for macOS Updates

Make sure your system is updated. Sometimes, updates include storage compatibility improvements.

6. Seek Professional Help

If the drive is physically damaged or critical data is at stake, professional data recovery services may be necessary.

Preventing Future Errors

Always eject disks safely before disconnecting.

Avoid using cheap or faulty cables and hubs.

Back up your data regularly to another drive or cloud storage.

Periodically check your drives for errors using Disk Utility or similar tools.

Conclusion

The “disk not readable by this computer” error can be alarming, but it doesn’t always mean your data is permanently lost. Often, the problem is related to formatting or minor corruption that can be repaired. By checking connections, using Disk Utility, and reformatting when necessary, you can restore functionality. For critical data, always attempt recovery before reformatting and consider professional help if the drive shows signs of hardware failure.