Double Data Rate 4 Synchronous Dynamic Random-Access Memory is a type of synchronous dynamic random-access memory with a high bandwidth interface.
Front and back of 8 GB DDR4 memory modules
A 16GB DDR4 SO-DIMM module by Micron
Synchronous dynamic random-access memory
Synchronous dynamic random-access memory is any DRAM where the operation of its external pin interface is coordinated by an externally supplied clock signal.
SDRAM memory module
SDRAM memory module, zoomed
The 64 MB of sound memory on the Sound Blaster X-Fi Fatality Pro sound card is built from two Micron 48LC32M8A2 SDRAM chips. They run at 133 MHz (7.5 ns clock period) and have 8-bit wide data buses.