Floating gate transistors

Floating gate MOSFET transistors use relatively high voltage to force few electrons into "floating gate" that is surrounded by non-conductive material like glass. Such memory storage can preserve data for many years without any electricity source and these floating gates are common in memory cards and Flash memory sticks or other chip shaped storages. While good at keeping data for long time they are slow at writing as capacitors have to charge up around 5-12 volt charge to push electrons there and later similar voltage is needed to push that electron out of floating gate. Fast computer memories like DRAM or SRAM read-write fast using about 1-1,5 volts but they lose data fast and DRAM has to rewrite its contents several times each second. These DRAM and other unstabler RAM memories use capacitors to hold charge but they leak their charge and this leaking happens faster with smaller capacitors so future RAMs may need to rewrite increasingly faster. 

Floating gates are filled with the help of control gate with varying charge that can pull or push electron to desired direction depending on if it used for writing, reading or erasing (last 2 are similar at first). Like other static electricity using memories that use electrons they lose their contents every time they are read because electrons get pushed out towards sensor and if data was detected in floating gate then it is usually automatically rewritten.