User Manual

DDR4 WHITE PAPER

Reduced Power Consumption

Power consumption is improved in multiple ways. First, there’s a baseline 20% reduction in

the voltage required to operate DDR4. While DDR3 requires 1.5V and DDR3L reduced this

requirement to 1.35V, DDR4 starts at 1.2V and is expected to receive a lower speciﬁcation in

the future that further decreases operating power.

Beyond that, DDR4 introduces additional power-saving technologies. DDR3 operates

at a single universal voltage speciﬁcation that then has to be scaled internally for some

operations. Increasing voltage internally generates heat, draws more power, and is

generally less ecient. DDR4 features a secondary voltage speciﬁcation, V

, operating at

2.5V. Instead of losing eciency by having to scale voltage, DDR4 has the needed voltage

available from the start.

DDR4 also adds multiple new refresh methods designed to reduce operating and idle

power consumption, and timings can be adjusted depending on DIMM temperature

to improve eciency and stability. This is more of a means of improving stability than

eciency, and while it won’t be implemented on standard UDIMMs, we can expect to see

this on RDIMMs and SODIMMs.

The DDR4 speciﬁcation allows for more ﬁnely grained control over power to the memory

itself. DDR3’s method of VDDQ termination, dubbed center tapped termination or CTT,

resulted in unused areas of memory still receiving power. DDR4 changes that by switching

to PODs, or Pseudo Open Drains, which eectively allows power to simply drain through

unused memory instead of being wasted.

The net result of these changes and additions to the speciﬁcation is that DDR4 can be as

much as 30% more ecient than DDR3 when operating at the same performance levels.

Increased Density

DDR4’s architecture was speciﬁed to allow for considerably higher IC and DIMM densities

than DDR3’s. Mainstream DDR3 DIMMs currently scale to 8GB, but a modiﬁed DDR3

speciﬁcation (Load Reduction DIMM) allows for an increase to 16GB or 32GB DIMMs. This is

unfortunately only visible chieﬂy on the enterprise side; while AMD’s processors can handle

16GB DIMMs, current generation mainstream Intel processors can’t support individual DDR3

DIMMs larger than 8GB.

The limitations of capacity in DDR3 are addressed from several angles in the DDR4

speciﬁcation, with each contributing to an overall massive improvement in potential

density.

First, while a DDR3 IC is speciﬁed for up to eight internal banks, DDR4 doubles this number

to 16 while also organizing them into four addressable bank groups (improving overall

performance and eciency). DDR4 also increases the potential density of the IC itself, all

the way up to 16Gb.