Skylake brings DDR4 into the mainstream. Orestis Bastounis investigates
New memory standards are launched far less frequently than new microprocessors, graphics cards or chipsets, so the use of DDR4 with 100-series chipsets and the Skylake platform is a milestone, being the first time a consumer chipset has used this type of memory. DDR3 has been around since 2007, where support for it debuted with Intel’s P35 chipset. With speeds ranging from 1333MHz up to over 2000MHz, the standard was a faster, more efficient evolution from DDR2 rather than a brand-new technology. SDRAM itself has been around for decades, with only relatively minor tweaks along the way.
DDR3 runs at 1.5v or 1.35v in its ‘DDR3L’ guise, while CAS latency times range between 7ns and 10ns depending on the module speed. A general rule is that faster memory has a higher CAS latency, but this difference is mitigated by the fact that faster clock frequencies have a much bigger impact on performance than latency timings.
When it launched, DDR3 was really expensive, and inflated the cost of upgrading to a new platform, but prices quickly normalised to the levels of its predecessor. The introduction of DDR4 follows a similar pattern. Speeds now range between 2133MHz and 3200MHz, with CAS latencies around 14ns. The required voltage has dropped to 1.2V and the modules use 288 pins, rather than DDR3’s 240 pins, preventing clumsy PC builders from accidentally putting the wrong type of memory in their computer.
Skylake supports both DDR4 and DDR3L, but Intel has stressed that DDR3L is only intended for low-cost devices where the use of DDR4 would inflate retail prices more than necessary. For gamers, or anyone buying a next-generation computer, DDR4 is the only way to go. If you weren’t aware, DDR3L and DDR3 are two entirely separate standards, so it’s unlikely you’ll be able to use your existing DDR3 memory in a Z170 PC anyway.
But thankfully, although DDR4 prices were initially high, they’re falling quickly. There’s still a small difference; 16GB of DDR4 RAM is very roughly 33 per cent more expensive than the same amount of DDR3 memory, but the price difference isn’t prohibitive.
Z170 also supports DDR4 modules with higher capacities than standard DDR3 modules. A DDR3 DIMM doesn’t have any more than 8GB of memory on it, giving you a maximum of 32GB in a consumer system with four memory slots. However, DDR4 modules have higher-capacity modules, with 16GB and 32GB DIMMs already on the market, and even mainstream Z170 motherboards such as the Asus Z170 Deluxe supporting up to 64GB of RAM. Unless you’re running loads of virtual machines, you’re unlikely to need so much memory at the moment, but 16GB kits now offer a good sweet spot for dual-channel systems.
The last question concerns frequency, so we ran our Realbench 2015 test suite on a 16GB Corsair Vengeance LLPX dualchannel DDR4 kit (pictured) running at both 2666MHz and 2133MHz. As we’ve seen before with memory tests, the performance difference wasn’t huge, but it was noticeable, particularly in our Gimp image editing test, which loads several high-resolution images into memory at the same time. In this test, the jump from 2133MHz to 2666MHz memory resulted in a 3.1 per cent performance increase. The difference was less pronounced in our other tests, but the end system score of 133,668 was still a few points ahead of the 132,978 from the 2133MHz memory.
As such, it’s fair to say that most people can get away with using slower memory without it having a drastic effect on realworld performance. However, at the time of going to press, 2666MHz DDR4 memory is very reasonably priced, with just £3 separating the price of a 16GB 2666MHz Corsair Vengeance LLPX dual-channel DDR4 kit and the same kit running at 2133MHz.