Dynamic random-access memory

Dynamic random access memory is the most commonly used form of RAM.

DRAM is called dynamic (or active), because it must be refreshed all the time or it will lose the data which it is supposed to be storing. Because it loses data when power is removed, DRAM is called volatile. This word comes from the Latin adjective volātilis, which means "flying, fleeting, transitory".

Refreshing DRAM means reading the data from the DRAM and directly writing them back to the DRAM. DRAM is made up of millions of very small capacitors. Each of these capacitors has a transistor to let energy in and out. The capacitor slowly loses energy, and if the DRAM is not refreshed, in the end one or more of the capacitors will let so much energy out, that for example a 1 will become a 0, so data will be lost or corrupted. Almost all computers refresh their DRAM many times per second.

Comparison DRAM and SRAM

DRAM is often compared to SRAM (Static RAM). SRAM is able to store data as long as power/energy is used. There is no need to refresh it. SRAM can also be faster than DRAM. But SRAM is much more expensive than DRAM. Also, SRAM uses more electric power and heats up much faster than DRAM. DRAM and SRAM lose the data when the power to them is turned off, unlike non-volatile random-access memory.

Dynamic Random-access Memory Media

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  A die photograph of the Micron Technology MT4C1024 DRAM integrated circuit (1994). It has a capacity of 1 megabit equivalent to 2^{20}bits or 128 KiB.

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  Motherboard of the NeXTcube computer, 1990, with 64 MiB main memory DRAM (top left) and 256 KiB of VRAM (lower edge, right of middle)

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  A schematic drawing depicting the cross-section of the original one-transistor, one-capacitor NMOS DRAM cell. It was patented in 1968.

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  The principles of operation for reading a simple 4 \times4 DRAM array

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  Basic structure of a DRAM cell array

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  DRAM ece385 illustrative example*I drew this with idraw for my ECE385 course, to illustrate how Dynamic random access memory (DRAM) works, with simple 4 by 4 array.

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  Self-aligned storage node locations simplify the fabrication process in modern DRAM.

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  A pair of 32 MB EDO DRAM modules

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  The die of a Samsung DDR-SDRAM 64-MBit package

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  MoSys MD908 MDRAM (multi-bank DRAM) chip of a Tseng Labs ET6000-based video card.