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Can you still use old hard drives with macOS Catalina?

If I upgrade my MacBook Air 2015 to macOS Catalina, will I still be able to access my several hard drives and old CD–ROMs?

Potential issues in accessing old external storage devices fall into three tiers: storage medium, file system, and format.

If a storage device connects to your Mac without relying on a special kernel extension, and works just with a regular USB or other port, then it should continue to work fine. Some specialized devices may rely on installing a kernel extension, which if it isn’t updated may not work, but instances of these are pretty unusual.

macOS Catalina supports all traditional file systems, including Mac OS Extended or HFS+ and the variants of DOS FAT, as well as featuring the latest improvements to APFS, so it shouldn’t have a problem. Any issues are most likely to arise in the file formats themselves, particularly old audio, still images, and video. Catalina has lost support for some old QuickTime compression formats, which Apple has outlined in bit.ly/ml163incmd. If any of your old documents use those formats, then accessing them in Catalina will be more tricky.