In which form does it store data?  DRAM is not the best, 
but it?s cheap, does the job, and is available almost 
everywhere you look. DRAM data resides in a cell made of a 
capacitor and a transistor. The capacitor tends to lose 
data unless it?s recharged every couple of milliseconds, 
and this recharging tends to slow down the performance of 
DRAM compared to speedier RAM types.

DRAM is a volatile memory made by capacitor and controlled 
by transistor.it needs periodical refreshment as the 
capacitor decays charge with time.