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The first DDR4 memory module prototype was manufactured by Samsung and announced in January 2011. [a] Physical comparison of DDR, DDR2, DDR3, and DDR4 SDRAM Front and back of 8 GB [1] DDR4 memory modules. 2005: Standards body JEDEC began working on a successor to DDR3 around 2005, [14] about 2 years before the launch of DDR3 in 2007.
DDR memory bus width per channel is 64 bits (72 for ECC memory). Total module bit width is a product of bits per chip and number of chips. It also equals number of ranks (rows) multiplied by DDR memory bus width. Consequently, a module with a greater number of chips or using ×8 chips instead of ×4 will have more ranks.
DIMM modules connect to the computer via a 64-bit-wide interface. Some other computer architectures use different modules with a different bus width. In a single-channel configuration, only one module at a time can transfer information to the CPU.
A memory rank is a set of DRAM chips connected to the same chip select, which are therefore accessed simultaneously. In practice all DRAM chips share all of the other command and control signals, and only the chip select pins for each rank are separate (the data pins are shared across ranks).
Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip; this space is occupied in ECC DIMMs. Three SDRAM DIMM slots on a ABIT BP6 computer motherboard. A DIMM (Dual In-Line Memory Module) is a popular type of memory module used in computers.
Those 64 bits are sometimes referred to as a "line." Number of interfaces: Modern personal computers typically use two memory interfaces (dual-channel mode) for an effective 128-bit bus width. For example, a computer with dual-channel memory and one DDR2-800 module per channel running at 400 MHz would have a theoretical maximum memory bandwidth of: