James Hunt assesses the benefits of the latest standard of RAM
It's been close to a decade since DDR3 memory was first introduced and five years since it became the dominant form of RAM in home PCs. In an industry where anything older than 18 months looks seriously out of date, DDR3 is starting to seem positively ancient. It's no surprise, then, that the next evolution of the technology, DDR4 memory, is starting to creep into the latest high-end hardware.
At this point, there's a chance that the next computer you buy will indeed support DDR4. But what is DDR4 memory, and what are the practical benefits of it? And most importantly, is it worth aiming to include in your next system?
What Is DDR4?
The RAM we use in our current computer systems is called SDRAM, which stands for 'Synchronous Dynamic Random Access Memory' - not that it matters much to consumers, because all RAM you can buy for your home computer is SDRAM. The bit where you get a choice is that your RAM can, at present, be either DDR3 or DDR4.
DDR is shorthand for 'Double Data Rate', and DDR4 is the fourth generation of that technology. It probably won't surprise you to hear that it was preceded by DDR3, DDR2 and standard DDR memory. DDR SDRAM works twice as fast as standard SDRAM, DDR2 is double that speed, and DDR3 is double that speed. DDR4, as you may have guessed, is twice as fast as DDR3.
As with previous RAM upgrades, DDR4 hardware is not compatible with any earlier versions due to a variety of factors. Different signalling voltage is one of the bigger reasons the two generations aren't compatible, but the modules will have a different physical interface to prevent any confusion. To use DDR4, you'll need a new motherboard entirely, and your old DDR3 modules will have to be thrown straight in the bin (or possibly sent somewhere more productive), because you're not going to be using them any more.
The majority of improvements in DDR4 are related to its speed. Faster clock frequencies allow greater data transfer rates, which speeds up memory access times, allowing faster framerates, loading times and data retrieval. DDR3 modules only officially support speeds up to 2133MHz, while DDR4 modules will start at 2133MHz and be rated up to 4266MHz.
In addition to this extra speed, DDR4's power usage is lower, because the modules run at a lower voltage - 1.05-1.2 volts, compared to 1.2-1.65 volts for DDR3. Lower power usage means better battery life for mobile devices, lower power bills and less heat inside a system, which is good news all around. DDR4 also supports a new technology called 'Deep Power Down', which means it can use near-zero power when in sleep mode, since no refresh is required to keep the data active. DDR4 also has the ability to refresh individual chips on a DIMM, rather than the whole DIMM, which can improve latency.
DDR4's improved speeds also allow it to support greater capacity modules. Last year, Hynix announced that it had developed a 128GB DDR4 module based on a 20nm process. Most DDR4 modules are likely to be 16GB a stick thanks to its higher-density chips, whereas DDR3 typically supports no more than 8GB. Larger-capacity modules do have a slightly higher latency compared to smaller ones, but the improvements in other areas cancel out any negative effects you might see.
In terms of physical appearance, DDR4 modules will have more pins on the connector (284 vs 240) but are the same length because the pins are closer together. The new modules are taller than DDR3, but only by less than a millimetre - 31,25mm, compared to DDR3's 30.35mm - and thicker than existing modules by 0.2mm, to allow for more signal layers. As for the SO-DIMM variants found in notebooks and other low-space/portable devices, they have 256 pins (rather than 204) and are 1 mm thicker, but have the same length and height as existing SO-DIMMs.
Can I Buy DDR4?
DDR4 modules have been on sale for a few months now, and it's entirely possible to walk into a shop and buy them today. But while you can buy DDR4, a much better question is whether you should or not.
The vast majority of current systems support DDR3 RAM, and if they don't, then they're probably DDR2. There's no point buying DDR4 on its own because it simply won't fit into your motherboard. Even if it could, the timings and power supply would be off in ways that would make it useless. To use DDR4 memory, you'll need to do a full upgrade of your system.
The only way you can install DDR4 modules at present is by basing your system on Haswell-E, Intel's latest 'enthusiast' platform. As well as introducing the new chip socket (called LGA2011-3), Haswell-E is the first home platform to offer DDR4 compatibility. Any motherboard based on Intel's X99 Haswell-E chipset will require DDR4 RAM. Meanwhile, AMD will support DDR4 when it releases its new Carrizo APUs and compatible motherboards, which was expected to be this year, but has recently been delayed until early 2016.
While upgrading to Haswell-E would of course result in a very powerful system that uses DDR4 memory, it'll also cost a lot of money. Crucially, the new RAM is going to represent only a tiny fraction of its improvements but a large proportion of its cost. 4GB of DDR4 RAM costs £50, which is double the price of DDR3.
Partly, that's because the first batches of DDR4 are intended for use in high-capacity systems, which means it has to be high-fidelity as well. Servers are likely to make the most use of DDR4, and it could be some time until home systems require RAM at speeds fast enough to make the price worth paying.
Between the cost and limited compatibility, DDR4 isn't going to become the industry standard any time soon, so there's no rush to get it in your system. Haswell's successor Broadwell is due in the next few months, but even that will still run on DDR3. Once again, only the enthusiast variant (Broadwell-E) will support DDR4, and that's aimed at people who demand the highest-capacity systems. DDR4 won't be supported by the standard consumer version of Intel's platforms until Skylake, which you can expect to see in mid to late 2016 at the earliest.
Ultimately, there's nothing about DDR4 that makes it an upgrade worth chasing right now. Unless you can demonstrate that low RAM speeds are causing a significant bottleneck in any particular task, DDR3 is still cheaper, more compatible and fast enough to stick with - for now, at least.
What About GDDR5?
If you're wondering how you can have DDR5 RAM in your graphics card when DDR4 has only just been released, then you're not alone - but the answer to this question is simple. The answer is that you don't.
The memory on graphics cards is actually GDDR5, not DDR5. GDDR means 'Graphics DDR' and although it sounds like a small variant of DDR, it's actually a distinct technology that's largely based on DDR3, with some enhancements that make it more suitable to graphics use. GDDR5 RAM isn't an abbreviation of 'Graphics Double Data Rate RAM (fifth generation)'; it's an abbreviation of 'Double Data Rate Type Five Synchronous Graphics Random Access Memory' - something totally outside the conventions of standard DDR's generational numbering.
Actual DDR5 (with no G) is not expected until to be available until close to the end of the decade - and that assumes the technology even lasts until then!