iMac 27" 2020 RAM

To start off, see > https://support.apple.com/en-us/HT201191

Then go to either OWC or Crucial for your RAM upgrade.

see > https://eshop.macsales.com/shop/memory/imac-2019-27-inch

and > https://www.crucial.com/compatible-upgrade-for/apple/imac-%28retina-5k--27-inch--2020%29-imac20-1

They are: 2666MHz DDR4 PC4-21300 

ONLY purchase RAM from either Crucial.com or Macsales.com. NEVER buy from anywhere else, why.....simple. iMacs are very sensitive to RAM and require very high quality RAM. Both of these vendors sell high quality products that work, have lifetime warranties, offer great pricing and service. In short, there is no reason to shop anywhere else.

By the way I installed 32 GB of Macsales.com RAM in my 2020 27" iMac, please not the pictures below to learn the orientation of which slots to use: