Dynamic random-access memory

Dynamic random-access memory (DRAM) stores each bit as electrical charge in a capacitor, accessed through a transistor. Because the charge leaks, the memory must be periodically refreshed.

DRAM cell: A DRAM cell stores one bit using a capacitor and an access transistor. Its capacitor holds the bit as charge, while the transistor connects it to the read circuitry.
Capacitor: An electrical component that stores energy in an electric field between conductive surfaces. Each DRAM bit is represented by charge held in a small capacitor.
DDR SDRAM: A family of synchronous DRAM that transfers data on both edges of the clock signal. DDR variants are the standard DRAM used as main memory in many computers.
Static random-access memory: Volatile memory that stores each bit in a bistable circuit without periodic refresh. SRAM avoids refresh but uses more transistors per bit, making it less dense than DRAM.
Sense amplifier: A circuit that detects and amplifies a small voltage difference on a memory bit line. It distinguishes a cell’s weak charge signal from the reference voltage during a read.
MOSFET: A voltage-controlled transistor widely used to switch and amplify electronic signals. A MOSFET in each cell controls access to its storage capacitor.
Graphics double data rate memory: A DRAM family designed for high-bandwidth graphics and accelerator workloads. Graphics processors use GDDR to move large volumes of image and computation data.
Flash memory: Nonvolatile semiconductor memory that stores data as electrical charge in isolated gate structures. Flash retains data without power, unlike DRAM, but has different speed and endurance tradeoffs.
DRAM refresh: The periodic operation that restores charge in DRAM cells before leakage erases stored data. Every cell must be refreshed because its capacitor cannot hold charge indefinitely.
Leakage current: Unwanted electric current that flows through or across an insulating barrier or inactive device. Leakage drains the stored charge and sets the need for refresh.

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