DDR SDRAM

DDR SDRAM
Double Data Rate Synchronous Dynamic Random-Access Memory

Comparison of DDR modules for desktop PCs (DIMM)
Front and back of a 1GB DDR SDRAM module for desktop PCs (DIMM)
Developer	Samsung[1][2][3] JEDEC
Type	Synchronous dynamic random-access memory
Generations	DDR2 DDR3 DDR4 DDR5
Release date	DDR: 1998; 27 years ago (1998) DDR2: 2003; 22 years ago (2003) DDR3: 2007; 18 years ago (2007) DDR4: 2014; 11 years ago (2014) DDR5: 2020; 5 years ago (2020)
Specifications
Voltage	DDR: 2.5/2.6 DDR2: 1.8 DDR3: 1.5/1.35 DDR4: 1.2 DDR5: 1.1

Double Data Rate Synchronous Dynamic Random-Access Memory (DDR SDRAM) is a type of synchronous dynamic random-access memory (SDRAM) widely used in computers and other electronic devices. It improves on earlier SDRAM technology by transferring data on both the rising and falling edges of the clock signal, effectively doubling the data rate without increasing the clock frequency. This technique, known as double data rate (DDR), allows for higher memory bandwidth while maintaining lower power consumption and reduced signal interference.

DDR SDRAM was first introduced in the late 1990s and is sometimes referred to as DDR1 to distinguish it from later generations. It has been succeeded by DDR2 SDRAM, DDR3 SDRAM, DDR4 SDRAM, and DDR5 SDRAM, each offering further improvements in speed, capacity, and efficiency. These generations are not backward or forward compatible, meaning memory modules from different DDR versions cannot be used interchangeably on the same motherboard.

DDR SDRAM typically transfers 64 bits of data at a time. Its effective transfer rate is calculated by multiplying the memory bus clock speed by two (for double data rate), then by the width of the data bus (64 bits), and dividing by eight to convert bits to bytes. For example, a DDR module with a 100 MHz bus clock has a peak transfer rate of 1600 megabytes per second (MB/s).