Dual Channel vs. Single Channel Memory

Single Channel vs Dual Channel MemoryThe hardware in Ultrabooks has been improving nicely generation on generation, with each update bringing improved performance, power consumption, design and choice for consumers.

On area that has seen particular attention has been in Intel’s focus on improving the performance of their integrated graphics solutions. They have gone from a state of trailing in terms of hardware features, poor driver support and risible performance, to offering compatibility with the latest DirectX feature levels and other major APIs, improved (although still not perfect) driver support and game compatibility, and performance that has increased steadily to the point that whilst not class leading it is close to competing integrated graphics solutions from AMD and low-end mobile discrete. This is particularly true in the latest generation Broadwell based chips with Gen 8 graphics.

One of the key limiting factors of integrated graphics solutions is the relative lack of memory bandwidth available to them. Currently most laptops ship with DDR3-1600 memory, giving 12.8GB/sec (64-bits per channel * 1600MHz / 8bits per byte) from a SODIMM module, with most processors supporting dual channel memory configurations which can work together to provide a total of 25.6GB/sec.

This may seem quite generous when compared to low-end discrete graphics solutions such as NVIDIA’s GeForce 820M and 840M which have just 16GB/sec available from their 64-bit DDR3-2000 memory, but it has to be remembered that the integrated graphics solution shares its memory between processor and graphics requirements, and that dealing with the vastly different types of memory accesses required by them brings its own overheads for the memory controller as well.

Disappointingly though I’ve found it has become more and more common for laptop manufacturers to ship systems with just one memory channel populated. This means the processor has to run in single, as opposed to dual, channel memory mode and halves the memory bandwidth to just 12.8Gbps (DDR3-1600) for both the CPU and graphics – less than low-end discrete graphics get dedicated to the GPU. This can have a very noticeable affect on gaming performance as demonstrated in the video below…

Ensuring you buy an Ultrabook with dual channel memory

For our testing we used an Intel NUC5i3RYH for ease of setup, but these configurations are often found in laptops with 4GB of memory, with manufacturers opting to install a single DIMM for the 4GB model and a pair for the 8GB version (if the RAM is socketed) to simplify their supply chain, however we’ve also seen a number of systems with single 8GB modules as well. If you have a system with just one DIMM module installed and a second DIMM socket in the machine then adding a second memory module can be a good way of unlocking some extra graphics performance in your computer.

Other systems have memory soldered to the laptop mainboard and so the configuration cannot be changed. Some, like the Dell XPS 13, come with this memory correctly configured in a dual channel arrangement for both 4GB and 8GB models, but it is always worth checking the manufacturers specifications if you are buying an Ultrabook and want to ensure optimal gaming performance.

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