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iMac (Retina 5K, 27-inch, 2019) DIMMs have a notch on the bottom, slightly left of the middle:.If your DIMMs are mixed in capacity, minimize the capacity difference between Channel A (slots 1 and 2) and Channel B (slots 3 and 4) when possible.
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iMac (Retina 5K, 27-inch, 2020) DIMMs have a notch on the bottom, slightly left of the middle.Find your model below for specific installation instructions and notch locations: When you insert a DIMM, make sure to align the notch on the DIMM to the DIMM slot.
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