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…
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.
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.
Yeah, I’ve never heard of that before either. What I have heard of is either MOA or MIL reticles. In that context a Mil stands for milliradian, which is a representation of angle. That definitely doesn’t track with the post though.
A couple old metrology equipment dated back from the 80s I still use calls them ‘mil’. It’s got dual dials for mil/mm. Gets me confused sometimes because the gauge can go down to couple millionths of an inch/couple 10s of nanometers.
In the design and manufacture of PCBs (aka circuit boards) a “mil” is a one thousandth of an inch, so it makes sense that’s what is being used in this context.
Also the maths check out: 0.005 inches is equal to aprox 0.12mm, “just over 0.1mm”.
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.
“we created the problem of soldered-on ram! now we have the solution: a new standard, for no fucking reason!” -every memory, board, and system company
But the article explains that there is a technical reason.
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.
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…
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.
For the curious (and lazy):
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.
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 …
What is a mil in this context? I’m genuinely curious.
Probably one thousandth of an inch.
I’ve heard it referred to as ‘thou’ but not ‘mil’
Yeah, I’ve never heard of that before either. What I have heard of is either MOA or MIL reticles. In that context a Mil stands for milliradian, which is a representation of angle. That definitely doesn’t track with the post though.
A couple old metrology equipment dated back from the 80s I still use calls them ‘mil’. It’s got dual dials for mil/mm. Gets me confused sometimes because the gauge can go down to couple millionths of an inch/couple 10s of nanometers.
LVDT for those curious.
A millimeter i.e a thousands of a meter.
edit: I was wrong, confusingly enough it is a thousands of an inch
5 mm isn’t ‘just over 0.1 mm’. That can’t be right.
Well, it depends on your margin of error.
In the design and manufacture of PCBs (aka circuit boards) a “mil” is a one thousandth of an inch, so it makes sense that’s what is being used in this context.
Also the maths check out: 0.005 inches is equal to aprox 0.12mm, “just over 0.1mm”.
I stand corrected, and I see I didn’t read the comment thoroughly enough either.
Colloquially as a non-pcb maker I would use and hear the term “mill” as short form millimeter so I assumed it was that.
so TIL :)
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.
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.
I meant PCBs. I design custom circuit boards.
Like this one: https://www.tindie.com/products/bmoreautomation/esp-r8-poe-3c-automation-controller/