Comment on iFixit hails replaceable LPCAMM2 laptop memory as a 'big deal'

• NOT_RICK@lemmy.world ⁨1⁩ ⁨month⁩ ago

  For the curious (and lazy):

  According to repair biz iFixit, the issue with the power-frugal LPDDR memory chips is that the lower voltage they operate at calls for more attention to be paid to signal integrity between the CPU and memory. In practice, this has meant shorter track distances on the circuit board, leading to LPDDR being soldered down as close to the processor as possible.

  LPCAMM2 is intended to address this by putting LPDDR onto a circuit board module that is “cleverly designed to mount right up next to the CPU,” with “very short traces to help maximize signal integrity,” the iFixit team explains in a blog and video detailing their hands-on with the ThinkPad P1 Gen 7.

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  • TimeSquirrel@kbin.social ⁨1⁩ ⁨month⁩ ago

    the lower voltage they operate at calls for more attention to be paid to signal integrity between the CPU and memory

    And they aren't kidding around, modern high speed signals are so fast that a millimeter or less of difference in length between two traces might be enough to cause the signals to arrive at the other end with enough skew to corrupt the data.

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    • SpaceNoodle@lemmy.world ⁨1⁩ ⁨month⁩ ago

      A millimeter is huge in these situations. USB3 requires 5 mil tolerances, just over 0.1 mm. This scales with the inverse of data rate.

      Electronics are so fast that we gotta take the speed of light into account. God help you if you put too sharp a bend in a trace, too …

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      • itsmect@monero.town ⁨1⁩ ⁨month⁩ ago

        USB3 is quite forgiving regarding the layout. The standard ±10% impedance matching is fine, and because there is no dedicated clock line you don’t need to do length matching either. Even differential pair length mismatch is not that big of a deal. If 0.1mm is easy to archive, sure go for it, but I’d rather compromise on this in favor of more important parameters.

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      • TimeSquirrel@kbin.social ⁨1⁩ ⁨month⁩ ago

        Haha, I'm still over here messing with 10/100 Ethernet and USB 2 on my home projects. I'm used to bigger tolerances than the truly high tech stuff.

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      • Threeme2189@lemmy.world ⁨1⁩ ⁨month⁩ ago

        What is a mil in this context? I’m genuinely curious.

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      • gregorum@lemm.ee ⁨1⁩ ⁨month⁩ ago

        That inverse square law will fuck you every time

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• agressivelyPassive@feddit.de ⁨1⁩ ⁨month⁩ ago

  I still don’t understand, why this is seemingly no problem in any other application.

  Desktops, servers and even some chonkier laptops manage to work with regular (SO)DIMMs just fine.

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  • farcaster@lemmy.world ⁨1⁩ ⁨month⁩ ago

    I’m guessing regular non-LP DDR works fine socketed in desktops because power is nearly a non-issue. Need to burn a few watts to guarantee signal integrity? We’ve got a chonky PSU, so no problem. On mobile devices however every watt matters…

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    • NaibofTabr@infosec.pub ⁨1⁩ ⁨month⁩ ago

      Plus the smaller chips (like the CPU) are designed for lower voltage and current. They can’t handle dialing up the power, they’ll melt.

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    • Aceticon@lemmy.world ⁨1⁩ ⁨month⁩ ago

      I recently got a have Mini-PC which a processor with a TDP of 6W and it uses run of the mill SODIMMS and the power supply for that stuff is a pretty regular wall socket power adapter, the same kind you would see for, say, a media box.

      I suspect it’s not even a few watts (at 3.3V 1W is around 300mA is quite an insane amount of current for a signal line), more like tens or even hundreths of a watt.

      Mind you, what really changes here is voltage rather than current: these things run at a lower voltage, which helps with speed and in reducing the power dissipating as heat (so they waste less power and heat up less) and that’s were signal integrity on longer signal traces becomes more of a problem because lower voltage signals are closer to the noise level the drop in voltage from the resistance of the circuit board lines because a higher proportion of the original voltage so the longer the trace the more likely it is that whatever reaches the other side is pretty much at the same level as noise.

      Still matches what you wrote, by the way, as power = voltage * current, so all else being the same lower voltage does mean less power consumed. It’s just that you were a bit off on the scale of the power consumption involved.

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  • lud@lemm.ee ⁨1⁩ ⁨month⁩ ago

    Normal DIMMs work fine but soldered RAM can just be much faster and in general better. It’s not an acceptable compromise on most desktops but for laptops which also has to be smaller and need to worry about stuff like battery life, it matters more.

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    • paraphrand@lemmy.world ⁨1⁩ ⁨month⁩ ago

      Sounds like there is a bunch of nuance in this topic!

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      • agressivelyPassive@feddit.de ⁨1⁩ ⁨month⁩ ago

        But I want clear black and white distinctions and outrage!!!

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  • fuckwit_mcbumcrumble@lemmy.dbzer0.com ⁨1⁩ ⁨month⁩ ago

    Laptops with sodimm DDR5 not only use much more power, but they’re also slower than LPDDR5.

    Ex: the Intel Thinkpad T16 has 5600mhz ram in sodimm form, but with soldered RAM (AMD version) it’s like 6400mhz.

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  • barsquid@lemmy.world ⁨1⁩ ⁨month⁩ ago

    My understanding is that those are slower (SODIMMs) or are able to use more power (DIMMs) to maintain signal fidelity.

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• wreckedcarzz@lemmy.world ⁨1⁩ ⁨month⁩ ago

  “they did it to save power!!! 111 one eleven”

  there was perfectly fine memory that was upgradable before. They (system integrators/oems) saw it as a way to kill the upgrade market, boosting profits.

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  • qjkxbmwvz@startrek.website ⁨1⁩ ⁨month⁩ ago

    “It’s more performant than the old SODIMM sticks, vastly more efficient, it saves space, and it should even help with thermals as well. All that, and it’s still about as repairable as anything we’ve ever seen,” iFixit concluded.

    Yes, there was a perfectly fine, upgradable memory standard before. And many 486s were also perfectly fine, upgradable computers.

    The fact that a new technology makes it so we can have our cake and eat it too — upgradability without any compromise — is a fantastic innovation.

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  • themachine@lemmy.world ⁨1⁩ ⁨month⁩ ago

    So you believe that the performance improvement and power saving is not worth creating a new standard?

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    • wreckedcarzz@lemmy.world ⁨1⁩ ⁨month⁩ ago

      No, not at the cost of locking in customer choice and flexibility. I have soldered-on ram in my ThinkPad, but not in my Predator gaming laptop. There is a -157% chance that Lenovo was trying to extract a few percent of extra speed so that I can open Firefox 0.13 seconds faster. Perhaps they’d try to cry “but battery life!”, in which case I’d respond with “well it’s not fucking working” as that machine barely gets 2.5h on a brand-new battery, browsing the web + terminal windows doing server admin stuff. (ThinkPad X13 Gen 2, Intel, with WWAN if you’re curious. Fucking 1.5k and it’s just passable for basic usage on the go.)

      I’m not really upset with this ‘new’ standard, but the fact that oems are absolutely going to use it as bullshit marketing “look, we fixed the problem! get our un-fucked ram for only $129 per stick!”. That’s what the fuck I’m pissed off about.

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      • themachine@lemmy.world ⁨1⁩ ⁨month⁩ ago

        I mean I’m not sitting here defending soldered on ram but your unnecessary aggression and sarcasm in your previous responses overshadows the fact that while solder on ram sucks for the upgrade and repair market the underlying tech has very tangible improvements and now we can maintain that improvement and the upgrade and repair functions.

        I agree, soldered ram is bad. But I disagree that LPDDR ram is fundamentally bad and this improvement allowing it to be modular while maintaining its improvements is a very good thing.

        As far as your complaints of battery life on your thinpad goes, there is much more to battery life than the consumption of the memory but naturally every part plays a role and small improvements in multiple places result in a larger net improvement. I’m assuming you’re running linux which in my experience has always suffered from less than optimal power usage. I’m far from an expert in that particular area but its always been my understanding that it is largely caused by insufficient fireware support.

        As a whole this looking at this article in a vacuum i only see good things. A major flaw with lpddr has been address and i will be able to expect these improvements in future systems.

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