DRAM

Dynamic random-access memory, or DRAM, is a type of volatile memory used primarily as the main system memory in computers and other digital devices. Each bit is stored as charge in a tiny capacitor within a memory cell, with access controlled by a single transistor. Because capacitors leak charge, the stored data decays over time and must be refreshed periodically, which is why the memory is described as dynamic as opposed to static RAM (SRAM).

The DRAM array is organized in a grid of rows and columns. A memory controller selects a row, then a column, and a sense amplifier reads or writes the cell’s charge. Access times, bandwidth, and densities have improved through generations that use synchronous operation and higher data rates. The common modern family is SDRAM and its successors—DDR SDRAM (DDR, DDR2, DDR3, DDR4, DDR5)—which transfer data on multiple edges of the system clock to increase throughput. Variants include LPDDR for mobile devices and GDDR for graphics, as well as newer stacked forms used in some high-bandwidth memory applications.

Refresh is a defining characteristic: periodic refreshing is required to maintain data. The memory controller issues refresh commands to restore the charge in each cell, often organized by rows; some devices support self-refresh to reduce power consumption when idle. DRAM’s advantages include high density and low cost per bit, which suit it for main memory, while its drawbacks include the need for periodic refreshing, higher latency than SRAM, and greater control complexity.