Which two types of SODIMM share a pin count?

The two types of SODIMM that share a pin count are DDR3 and DDR4 SODIMMs, both of which have 204 pins. Despite having the same pin count, they are not interchangeable due to differences in their signaling and voltage requirements. DDR3 operates at 1.5V, while DDR4 uses 1.2V, necessitating careful compatibility considerations when upgrading or replacing memory modules.