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469

iFixit hails replaceable LPCAMM2 laptop memory as a 'big deal' (www.theregister.com)

submitted 6 months ago by [email protected] to c/[email protected]

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[–] [email protected] 90 points 6 months ago (29 children)

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.

[–] [email protected] 76 points 6 months ago* (last edited 6 months ago) (28 children)

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 time skew to corrupt the data.

Edit: if you ever looked closely at a circuit board and seen strange, squiggly traces that are shaped like that for seemingly no reason, it's done so that the lengths can be matched with other traces.

[–] [email protected] 47 points 6 months ago (27 children)

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 ...

[–] [email protected] 6 points 6 months ago (2 children)

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.

[–] [email protected] 7 points 6 months ago

Same, but now I'm working on very high-speed stuff for work and starting to get into that hobby-wise as well. Just yesterday had a conversation with a colleague about how things are getting too small to hand-solder.

[–] [email protected] -3 points 6 months ago (1 children)

My dedicated AI machine uses 1866mhz DDR3. Consumers don't know what they need and will buy whatever the latest new thing is. Smart phones are so dumb. Like wow, your brand new $2500 phone has a benchmark 4x faster than my refurbished $250 phone. Now tell me what you do with all that power. "...well I save 27ms per Instagram post which adds up with how much I use it". I want to run headfirst into a brick wall.

[–] [email protected] 12 points 6 months ago* (last edited 6 months ago)

I meant PCBs. I design custom circuit boards.

Like this one: https://www.tindie.com/products/bmoreautomation/esp-r8-poe-3c-automation-controller/

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