DRAMs

Dynamic random-access memory, or DRAM, is a class of volatile computer memory used primarily as the main memory in many computer systems. DRAM stores each bit as an electrical charge on a tiny capacitor within a memory cell, with a single transistor providing access to the capacitor. Because capacitors leak charge over time, the stored data must be refreshed periodically to preserve it. This refresh requirement distinguishes DRAM from static RAM, which does not need periodic refreshing.

In a DRAM array, memory cells are organized into rows and columns. Access to a row is controlled by a word line, while bit lines carry data to and from the sense amplifiers. Reading a bit is typically a destructive operation, meaning the original charge is altered during sensing, so the data must be rewritten to the cell after a read. The refresh cycles are coordinated by the memory controller to maintain data integrity without interrupting normal operation.

DRAM has evolved from asynchronous to synchronous designs. SDRAM, introduced in the 1990s, synchronizes with the system clock and laid the groundwork for higher-bandwidth generations such as DDR, DDR2, DDR3, DDR4, and DDR5. Modern DRAM also includes mobile and low-power variants, and increasingly, 3D-stacked configurations and high-bandwidth memory modules to boost bandwidth and density.

Key advantages of DRAM include high storage density and lower cost per bit compared with static RAM. Its main drawbacks are the need for continual refreshing, higher latency relative to SRAM, and higher power usage per bit. DRAM remains the dominant technology for system memory in PCs, servers, and many consumer electronics applications due to its favorable price-performance balance and scalability.