In 1966 Robert H. Dennard invented Dynamic Random Access Memory (DRAM) cells, one-transistor memory cells that store each single bit of information as an electrical charge in an electronic circuit. This technology permitted major increases in memory density.
DRAM is a type of random access memory that stores each bit of data in a separate capacitor. The number of electrons stored in the capacitor determines whether the bit is considered 1 or 0. As the capacitor leaks electrons, the information gets lost eventually, unless the charge is refreshed periodically.
Since then capacity was increased thousands of times and access time was reduced dramatically.