DDR3 vs DDR4 - Games Weekly

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Saturday, October 25, 2014

DDR3 vs DDR4

DDR4 is here and it couldn’t have come at a better time, coinciding with the release of the first desktop 8-core CPU. In the next couple of years, all platforms will transition to this new memory standard, primarily because of power efficiency and performance. The differences for the desktop are fairly obvious with DDR4 officially starting where DDR3 stopped. If the previous memory standards are anything to go by, performance over the next decade will increase tremendously while capacities and power draw diminishes appropriately. It’s important to note that DDR4, while sharing the same physical dimensions as DDR3, has a diff erent notch, pin count and operating voltage, thus they are incompatible.

DDR4 uses 288 pins and operates at 1.2V as opposed to DDR3’s 240 pins and 1.5V operating voltage. DDR4 is currently supported on the Intel HEDT X-99 and Socket 2011-3 platform exclusively. In Q3 of 2015 however, the Z170/LGA 1151 performance platform will transition to DDR4 as well. AMD should follow suit with their new products in 2016. Below are some basic diff erences between the two memory types that should give you a more practical understanding of what this means for you and your computing devices.

Consumer or desktop DDR3 modules are generally limited to 8GB per DIMM, so kits are usually anywhere between 2x1GB all the way to 8x8GB. Realistically that means the most amount of memory any one desktop system can have is 64GB. This is plenty of memory and even though memory requirements have increased substantially since the introduction of DDR3, it’s tapered off , and at present there are many modern functional machines with 4GB of memory total. With that said, this may not be the case going forward and increasing memory capacity in a cost effective way has hit its limits. What DDR3 offers at present is still more than enough for gamers and the most demanding power users. At present the average memory capacity for gaming systems is 8GB, configured as 2x4GB DIMMs.

Hard to believe but DDR3 is seven years old, giving it a much longer lifespan than both DDR and DDR2 memory. It’s gone from requiring 1.8V for the early 1GB sticks to the more commonly used 1.5V memory. low voltage DDR3 (DDR3LV) has further decreased this to 1.35V allowing it to be used within TDP limited devices and platforms. Frequencies have also gone from a lowly 1,066MHz right up to 3,200MHz kits. These are rare and costly but they are on the market and can be purchased at most major retailers.

Real world performance has improved with the refinement of memory controllers and improved caches and caching mechanisms within the various CPUs. Latency has increased in favour of frequencies, but modern day systems benefit more from the higher frequency and increased bandwidth. 2,666MHz seems to be the ideal frequency for most systems where there are just enough wait states to not compromise overall performance, but off er plenty of bandwidth as well. For interests sake bandwidth at this speed is anywhere between 21.3GB/s to a hair over 85 GB/s in theory. Most systems will utilize around 70% of the available theoretical bandwidth. What’s great about DDR3 is that its long life has allowed vendors to fine tune its performance to where it is offering very high efficiency thus keeping itself relevant far surpassing its intended life cycle.

A huge selling point for DDR4 is that DRAM capacities per module can be as high as 16GB with some working, demo 32GB DIMMs scheduled for release in the near future. In theory, at least for the desktop and supporting platforms, this allows up to 128GB of system memory. What this change will likely do is grow the average system memory capacity from 8GB to 16GB, while simultaneously
allowing single CPU servers greater capacities via UDIMMs. 

DDR4 officially starts at 2133MHz which is the limit for DDR3 according to the JEDEC specification. Not that this means much because the vast majority of DDR4 modules on the market are 2400MHz or higher with some from G.Skill reaching 3,333MHz already. In DDR4’s lifespan these frequencies will climb well above the 4,200MHz mark. Other than frequency and capacity, the major benefit for DDR4 is its low power requirements compared to its predecessor. DIMMs
usually operate at 1.2V with an unofficial DDR4 low voltage spec citing voltages as low as 1.05V. Lower heat output, operating voltage, power draw and higher frequencies mean DDR4 is better than DDR3 in all meaningful ways. It is also suitable for use in different devices from smart phones to servers, with only the form factor changing of course. As far as logic and implementation is concerned however, it is consistent across the various platforms.

At present the only existing desktop system memory controller allows anywhere between 50 to 70% of the theoretical bandwidth utilisation. This is system side however and is not related to how well DDR4 modules will perform on other systems. The only existing memory controller is in its first iteration and they will improve over time along with the DRAM frequencies, thus it is feasible to reach the same efficiency levels in future as with DDR3 and possibly higher with systems delivering over 100GB/s in system bandwidth.

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