My friend wants to upgrade the OS yet still run some important yet old applications which can only run on Tiger - the idea behind two partitions is to be able to have both OSs available at boot time on the Mac's partitioned HD.
The HD currently is one partition with Tiger which OS cannot partition on the fly.
iMac (Retina 5K, 27-inch, 2017); 3.8 GHz Intel Core i5; 2TB HD; 64 GB 2400 MHz DDR4 RAM; Radeon Pro 580 8 GB. iPad Pro 10.5" Model MPME2B/A with 512GB capacity; iPhone SE 2020 256GB
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