Definition: dynamic RAM

The most common type of computer memory and generally available today in the form of synchronous dynamic RAM chips (see SDRAM). Most all volatile memory is dynamic RAM because it uses only one transistor and one storage capacitor for each bit. It is denser and much less costly than "static RAM," its faster counterpart.

Dynamic RAM Is a Total Loser
Unlike non-volatile firmware chips (flash, ROM, EEPROM, etc.), which hold their contents when the power is turned off, both dynamic RAM (DRAM) and static RAM (SRAM) require constant power.

The capacitors in a dynamic RAM chip are electrical storage tanks that do a poor job of holding a charge. They constantly leak, and the memory chip would lose its content were it not for the refresh circuitry that continuously re-energizes the capacitors approximately 15 times per second.

In 1968, dynamic RAM was patented by IBM, and the first commercial chips came from Intel and Mostek in the early 1970s with a capacity of 1,000 bits. See static RAM and memory types.

A Dynamic RAM Cell

DRAM cells are very simple. The combination of voltage on the row and column lines charges a capacitor. The only problem is that the capacitors keep losing their charges, and the bits must be read and re-written to the same state several times each second.