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 (1×32-bit channel), DDR5 SDRAM (2×32-bit subchannels), and upcoming DDR6 SDRAM (with 4×16-bit subchannels), 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.

In 2026, a cost-reduced HUDIMM was introduced, with only one 32-bit channel, not the usual two subchannels (and thus also half the bandwidth and capacity of DDR5), compatible with some DDR5-using motherboards. Another adaptation to skyrocketing memory prices (caused by AI boom) are adapters to use cheaper laptop memory in desktop computers.

DDR memory is used in laptops, desktops and servers, in different (DIMM) form factors; and usually unbuffered, not registered, except in servers. CUDIMM is a desktop memory (form factor) introduced for DDR5 in 2024, clocked (and unbuffered), while registered memory exist (for servers), and faster DDR5 MRDIMM; and generation 2 and 3 of MRDIMM upcoming).

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).