While they offer fast speeds, solid-state drives (SSDs) are still pricey, and your costs can suddenly increase if you want to boost the storage when buying a Mac mini or an iMac. However, both Macs support high-performance USB 3 and Thunderbolt 3, and you can use this help offset the costs of getting more storage.
If the prices for high-capacity SSD upgrades for the Mac mini and iMac make you balk, you can get a more affordable external USB 3 or Thunderbolt 3 hard drive. Then, to get the most out of the speed of the SSD in the Mac mini or iMac, you can split your system and apps to one drive, and your user files to another.
With a Mac mini, the two standard configurations come with a 128GB or 256GB SSD, which you use to storage macOS. Then you attach a high-capacity external drive (SSD, hybrid, or even a fast hard drive) for your user files, which would include music and photos.
With an iMac, you’ve got options depending on which model you choose. On the two lower-end iMacs, opt for a 1TB Fusion drive (a $100 upgrade), and hold user files there, while using an external lower-capacity external SSD for your system. On the highest-tier iMac, pick a 256GB SDD (also just $100 more than the 1TB Fusion drive) for the system and use an external high-capacity drive for user files.
Read more at MacWorld.com