DRAM
A memory cell that stores one bit as charge on a capacitor. Simple and cheap to make, it serves as the main memory of computers.
In the late 1960s Robert Dennard at IBM devised a circuit that stores one bit with just one transistor and one capacitor, patented in 1968[1]. Charge present or absent stands for 1 or 0. The charge leaks away slowly, so each cell is constantly read and rewritten before it fades, which is why the memory is called dynamic.
With so few parts per bit, a great deal of memory fits in a small area. The contents vanish when the power is switched off. In the 1980s Japanese makers took most of the world market on quality and yield, which led to trade friction with the United States. Today three companies, in South Korea and the United States, produce nearly all of it.
Related terms
- TransistorA semiconductor device in which a small signal controls a larger current, so it can amplify or switch. The basic component of all electronics.
- MOS transistorA transistor built from a metal electrode, an oxide layer and a semiconductor, in which a voltage on the electrode alone opens and closes the channel. Most of today's chips are made of these.
- Dennard scalingThe design rule that shrinking a transistor's dimensions and voltage by the same factor makes it faster and more efficient while keeping heat per unit area constant.