Hello.   Yes, they can be mixed. However, the 8 4Rx4 which is a Quad Rank memory module has to be installed first; i.e on the slots with white sleeves and then 8 1Rx4, a Single Rank module.
Hi, We have a PowerEdge T620 that came with 32GB ram, 4x 8GB 1Rx4 DIMMs (Hynix HMT41GR7AFR4A). We have upgraded to 64GB with 4x 8GB 1Rx4 DIMMs (Samsung M393B1G70BHO).  We have now upgraded again to 384GB with 12x 32GB 4Rx4 DIMMs (Hynix DELL server memory 32GB DDR3 1600MHz 4Rx4 1.35V QRLVRD) I still would like to keep the 8GB modules. Is it possible to mix 8 1Rx4 with 8 4Rx4 and if so which slots should I use? Would there be any backdraws? Or shall I sell them? Thanks!
T620 mixing 4Rx4 & 1Rx4 DIMMs