Problems between two macOS versions
EDITED BY HOWARD OAKLEY
Q I keep my internal disk running Mavericks, and an external SSD with Mojave installed. How can I switch between them using the Startup Disk pane?
by WILL DEWAR
A It’s normally possible to dual-boot in this way between two close versions of macOS, but doing so with 10.9 and 10.14 is inevitably difficult. The reason is Apple’s new file system, APFS: this wasn’t introduced until High Sierra, and Mavericks can’t recognise or mount any volume in APFS format.