Mobile DDR or mDDR or Low Power DDR or LPDDR memory is a low power and low size version of the Double Data Rate Synchronous Dynamic RAM used in Personal computers. The original DDR RAM memory used in PCs are consume large area on the computers motherboard and hence are not suitable for use in SMART phones or mobile systems as the space available for mounting the memory in handsets is very less due to their small size.
The original DDR memory looks like this,
The DDR memories are versioned DDR1, DDR2, DDR3 which are not compatible with each other and add more improved functionality in terms of speed, cost reduction , size etc. The LPDDR memory is optimized for performance at low power and size, The LPDDR operating voltage has been significantly reduced from 2.5V to 1.8V. The LPDDR adds more power saving features like Temperature compensated refresh ( because DRAMs require refreshing less often at low temperatures) , Partial array self refresh and "Deep power down" mode in which all the memory contents are wiped off. And LPDDR memories give significant size reduction and board space savings than their PC equivalents. The main providers of LPDDR memories are Samsung and Micron. LPDDR chip looks like this,
The mDDR memories are used in most of the today's SMART phones and tablets and are available in PoP memory forms to get more board space savings.