Dynamic random-access memory

Dynamic Random-Access Memory (DRAM) is a type of random-access memory used in computing devices for storing data. It is called "dynamic" because it needs to be periodically refreshed to retain data, unlike static random-access memory (SRAM) which does not require refreshing. DRAM is widely used in digital electronics where low-cost and high-capacity memory is required.

Overview

DRAM stores each bit of data in a separate tiny capacitor within an integrated circuit. The capacitor can either be charged or discharged; these two states are used to represent the two values of a bit, commonly referred to as 0 and 1. However, capacitors leak charge, and therefore, the information eventually fades unless the capacitor charge is refreshed periodically.

Because of its structure, DRAM is a type of volatile memory: when the power supply is turned off, the stored data is lost. Despite this, DRAM is extensively used for the primary storage in computing systems, including personal computers, workstations, and servers, due to its high speed and low cost compared to other types of memory.

History

The concept of DRAM was invented by Dr. Robert Dennard at IBM in 1966. The first commercial DRAM chip, the Intel 1103, was introduced in 1970. It had a capacity of 1 kilobit and was a significant improvement over the then-used magnetic-core memory in terms of both cost and performance. Since then, the capacity of DRAM chips has increased exponentially, following Moore's Law, with sizes now reaching multiple gigabits.

Operation

The basic operation of DRAM involves three steps: charge, store, and refresh. To write data, the DRAM cell is charged or discharged, representing a 1 or a 0, respectively. To read data, the charge stored in the capacitor is transferred to a sensing amplifier. Because this read operation is destructive, meaning the information is lost once read, the value must be written back or refreshed.

The refresh operation is critical to DRAM's functionality. All cells in the DRAM must be refreshed at regular intervals, typically a few milliseconds, to prevent data loss. This is achieved by reading the data from each cell and immediately writing it back.

Types of DRAM

Several variations of DRAM have been developed to improve performance, reduce power consumption, and increase density. These include:

• Synchronous DRAM (SDRAM): Synchronizes the memory's operations with the CPU clock, improving speed.
• Double Data Rate SDRAM (DDR SDRAM): Transfers data on both the rising and falling edges of the clock signal, effectively doubling the memory bandwidth.
• Graphics Double Data Rate SDRAM (GDDR SDRAM): Designed for graphics cards, offering higher bandwidth than standard DDR SDRAM.

Applications

DRAM is used in virtually all computing devices that require large amounts of fast-access memory. This includes personal computers, where it serves as the main system memory, as well as in servers, workstations, and graphics cards. DRAM is also used in some embedded systems and consumer electronics, such as digital cameras and gaming consoles.

Challenges and Future Directions

As devices require more memory, the physical limitations of DRAM become more apparent. Issues such as power consumption, heat generation, and data retention are significant challenges. Researchers are exploring new memory technologies that could potentially replace or complement DRAM, such as Magnetoresistive Random-Access Memory (MRAM) and Resistive Random-Access Memory (ReRAM).

See Also

• Computer memory
• Memory refresh
• Non-volatile memory