Comment on iFixit hails replaceable LPCAMM2 laptop memory as a 'big deal'
NOT_RICK@lemmy.world 6 months agoFor 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.
TimeSquirrel@kbin.social 6 months ago
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.
SpaceNoodle@lemmy.world 6 months 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 …
itsmect@monero.town 6 months 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.
gregorum@lemm.ee 6 months ago
So, does it just have really advanced error checking? How does it handle the mismatches?
AnUnusualRelic@lemmy.world 6 months ago
That’s why serial busses won over parallel ones I guess.
TimeSquirrel@kbin.social 6 months 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.
SpaceNoodle@lemmy.world 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.
GluWu@lemm.ee 6 months ago
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.
Threeme2189@lemmy.world 6 months ago
What is a mil in this context? I’m genuinely curious.
Hawke@lemmy.world 6 months ago
Probably one thousandth of an inch.
flying_gel@lemmy.world 6 months ago
A millimeter i.e a thousands of a meter.
gregorum@lemm.ee 6 months ago
That inverse square law will fuck you every time