The iMac 27-inch (2020) takes up to 128GB of user-upgradeable DDR4 RAM

Unlike most modern all-in-ones, the 27-inch iMac (2020) has a RAM door on the back — four accessible SO-DIMM slots that support up to 128GB total (four 32GB modules of 260-pin DDR4 at 2666MHz). It’s one of Apple’s most user-friendly designs in recent years, letting you buy base RAM from Apple and upgrade later with off-the-shelf kits for a fraction of the price.