Can I mix DDR3 and DDR4?

Can I mix DDR3 and DDR4? No. Completely impossible. Even if motherboard has both types of DIMM slots (some older models) only one of them can be used at a time. DDR2, DDR3 and DDR4 all run at different voltages.

No. Completely impossible. Even if motherboard has both types of DIMM slots (some older models) only one of them can be used at a time. DDR2, DDR3 and DDR4 all run at different voltages.