Apple Expert

The one-stop column for Genius advice

I have an imac (Retina 4K, 21.5-inch, late 2015) and it is very sluggish running macos Big Sur. Can I upgrade it to run faster?

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Unfortunately, these imacs cannot be upgraded with more memory as they’re sealed units with solderedon RAM. However, you could consider purchasing a sizeable external HD and then running macos from that. If you turn to page 36 now you’ll find a complete guide to setting up and running Big Sur from an external HD, which we can confirm works very well indeed.