From a physical standpoint, DDR4 is the same width as DDR3, but is slightly taller by about .9mm. The main physical difference between DDR3 and DDR4 is that DDR4 uses 288 pins compared to the 240 pins on DDR3 and the key is in a different location. Though there are ton of changes, the four major improvements of DDR4 SDRAM can be summed up in lower operating voltage, increased power saving enhancements, increased frequency, and improved chip density.



Link: TechSpot