Physical Differences DDR3 RAM modules have 240 pins while DDR4 kits have 288 pins. The key notch is slightly more to the right on DDR3 RAM modules while on DDR4 modules, it is more centralized. Motherboards are usually exclusively compatible for either RAM type due to their physical differences, so checking for compatibility before buying a new RAM kit is usually a good idea. A few motherboards do offer compatibility for both memory types. Speed RAM clock speed is the frequency at which the module operates. Less frequency is slower while higher frequency is better. The frequency shows the number of mega transfers the RAM module does in 1 second.