No, you can't interchange DDR3 into DDR4 slots (or vice versa). There are motherboards, like the one linked below that contain both types of slots. You can use only one memory type at a time, typically, with these hybrid systems:
No, you can't interchange DDR3 into DDR4 slots (or vice versa). There are motherboards, like the one linked below that contain both types of slots. You can use only one memory type at a time, typically, with these hybrid systems: