Memory makers have been showing off DDR4 memory modules for months. The final specification covering the replacement for DDR3 was only finalized today, though. The JEDEC group that oversees memory standards has published the DDR4 spec, which can be downloaded here. Registration is required to grab the 214-page PDF, but the highlights can be seen on this page of JEDEC's site. Here's a taste:
The per-pin data rate for DDR4 is specified as 1.6 giga transfers per second to an initial maximum objective of 3.2 giga transfers per second. With DDR3 exceeding its original targeted performance of 1.6 GT/s, it is likely that higher performance speed grades will be added in a future DDR4 update. Other DDR4 attributes tightly intertwined with the planned speed grades, enabling device functionality as well as application adoption, include: a pseudo open drain interface on the DQ bus, a geardown mode for 2,667 MT/s per DQ and beyond, bank group architecture, internally generated VrefDQ and improved training modes.
The DDR4 architecture is an 8n prefetch with two or four selectable bank groups. This design will permit the DDR4 memory devices to have separate activation, read, write or refresh operations underway in each unique bank group. This concept will also improve overall memory efficiency and bandwidth, especially when small memory granularities are used.
Although the specification has been finalized, we probably won't see DDR4 make a dent in the DRAM market for some time. iSuppli expects DDR4 to make up only 12% of the module market in 2014—and none of it before then. In 2015, the firm anticipates over half of the memory modules sold will have DDR4 chips onboard.
New memory types tend to be comparatively expensive to start, so a slow transition to DDR4 isn't a bad thing. Existing DDR3 memory seems plenty quick for desktop systems, and it's affordable enough that 16GB configurations can be had for less than $70 right now.