The push for smaller and thinner laptops, Ultrabooks, and tablets of late has come with some potentially undesirable side effects, namely the loss of flexibility. Of the Ultrabooks we’ve reviewed, I’m not sure any supported more than a single SO-DIMM slot for memory expansion, and many of them have all the DRAM components mounted directly onto the motherboard, all in the pursuit of reducing the z-height of the systems. In an effort to provide something of a middle ground, both Micron and TE Connectivity are offering alternatives that provide some reduction in z-height compared to standard SO-DIMMs while still maintaining the flexibility of an SO-DIMM slot.

The solution is quite simple and maintains full backwards compatibility with standard SO-DIMM slots, but to fully realize the z-height savings a modified SO-DIMM socket is required. In short, Micron is offering single-sided SO-DIMMs (with a standard 4GB capacity); since there are no components on one side of the SO-DIMM, it can lie flat against the motherboard. This is where the new SO-DIMM socket comes into play: it would have the module sit nearly flush against the motherboard so the connector would be the same but the housing would be slightly different.

To put things in perspective, a standard SO-DIMM is around 4mm thick; the new single-sided SO-DIMMs are able to reduce the z-height to 2.6mm. That’s not to say that they’re able to match surface mounted DRAM (around 1.2mm), but users and manufacturers would be able to choose between several memory configurations (generally speaking, 4GB or 8GB) and still maintain a thin profile. With surface mounted DRAM, you get the thinnest profile but completely lose out on upgradeability and if a company wants to offer two SKUs (e.g. 4GB and 8GB) it requires more effort in the manufacturing and assembly process. There’s also the potential for DRAM failures, which are simple to fix if you have a module but require a new board if you have surface mounted components.

From a high level, I’d just as soon see all modern laptops ship with 8GB standard, particularly the Ultrabooks with surface mounted DRAM, but manufacturers are always looking for ways to reduce cost and that has led to the existing crop of 4GB non-upgradeable Ultrabooks (ASUS UX21A/UX31A, Acer S7, etc.) One other item of note is that all of the reduced z-height modules from Micron will be reduced standby (1.35V DDR3L-RS). At least initially, the modules will only be shipping in 4GB capacities (currently, 8GB SO-DIMMs require dual-sided modules). Future higher density modules with monolithic devices (8x8Gb) should show up eventually, and of course all of the design elements are applicable to DDR4 when we see a shift to that some time likely next year.

This particular approach is only one of several that are apparently being tossed around in the industry, but thanks to the backwards compatibility with existing SO-DIMM slots it appears to have a better chance of succeeding. Other approaches that are being looked at right now include non-standard modules, which would require new connectors and modules and likely limited production compared to existing solutions. It’s expected other companies will also support the new connector, and availability of the new package (connector and single-sided SO-DIMMs) is expected this spring.

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  • MrSpadge - Thursday, February 7, 2013 - link

    A small step, but a nice one nevertheless!
  • DanNeely - Thursday, February 7, 2013 - link

    instead of sticking the sodimm on top of the board, put the connectors on the edge and install the ram in plane with the mobo instead of parallel with it.
  • Zink - Thursday, February 7, 2013 - link

  • Zink - Thursday, February 7, 2013 - link

    But then you get a smaller motherboard PCB because you can't run traces or put components under the DIMMs.
  • DanNeely - Thursday, February 7, 2013 - link

    soldered on chips already cost the surface of the board; if needed the additional area for traces could be covered by adding another layer to the PCB or by not allocating 100% of the next round of board shrinkage to batteries.
  • Sivar - Thursday, February 7, 2013 - link

    Adding another PCB layer is not a decision to be made lightly for cost and complexity reasons.
    If the board can be designed so that it is still small and doesn't need the extra PCB space, many manufacturers would still prefer to make it that much smaller and still use surface-mount or perhaps Micron's solution, depending on the design.
    I still like the idea though. It makes sense for SKUs meant for higher-end users which are meant to be upgradeable.
  • ajp_anton - Thursday, February 7, 2013 - link

    What's wrong with 4GB modules? We want dual-channel, so that should result in 8GB total anyway, which is perfect for the thin laptops these are made for.
  • JarredWalton - Thursday, February 7, 2013 - link

    Nothing, and I think 8GB total is a good target. I'm merely pointing out that at least initially, 8GB modules aren't an option (for those that might need more than 8GB).
  • ajp_anton - Thursday, February 7, 2013 - link

    OK. It seemed like you were disappointed at the small 4GB modules =).
    I just think that the person who needs 16GB also needs a faster CPU and therefore needs a thicker chassis that already has room for the RAM.
  • JarredWalton - Thursday, February 7, 2013 - link

    Fire up Photoshop and open 20 images for editing (like, say, at a tradeshow) and more memory will be very beneficial. I'm not saying everyone needs to do that sort of workload, but there is no such thing as "one size fits all". "One size fits most", sure, but not all. :-)

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