7 ms·

> In a universe where you want high-performance energy efficient RAM [.....] You simply can’t have this with socketed RAM. You make it sound like a prerequisit

by tomxor 5y ago

> In a universe where you want high-performance energy efficient RAM [.....] You simply can’t have this with socketed RAM. You make it sound like a prerequisite. I'm pretty sure the reason LPDDR is Low Power is not due to (currently) being unavailable in socketed modules - that would seem to be a side-effect of the original target market (smart phones). They are just some BGA packages, I see no reason they couldn't be soldered onto a board with a socket. If you scan through the features that make LPDDR LP, they have nothing to do with sockets, or anything affecting sockets: lower operating voltage, more power states, partial refreshing etc: https://en.wikipedia.org/wiki/LPDDR https://en.wikipedia.org/wiki/LPDDR

baybal2 5y ago
Yes, as I wrote somewhere below, LPDDR4 signal is actually more robust than DDR4 signal, and LPDDR4 controllers have more features to fix degraded signals. DDR5 has more roots in the LPDDR4 than in the regular DDR4.
ribit 5y ago
LPDDR is low power because it is a more sophisticated device with more complex protocol compared to regular DDR, because it has a higher pinout allowing it to have a more efficient electrical connection and because the computer manufacturer can optimize the connection with specific chips in mind instead of having to support a wide range of devices. I think the number of pins is a practical limitation. Current DDR DIMMs use 260-280 pins if I remember correctly, while an average LPDDR4X BGA package is 400 balls or higher. Apple uses chips with 877 balls. It is definitely possible to design modular RAM with high-pinout, but would it be economically feasible?
- rthomas6 5y ago
  It is if it's a standard that everyone decides to support...
  - ribit 5y ago
    That's the thing, who is everyone? Such technology would only be relevant to premium-level ultraportable notebooks. Desktops, gaming laptops as well as budget laptops would stick with the cheaper and more ubiquitous DDR. Smartphones and tables will continue to solder RAM on due to space constraints. Apple (who is the driving force in this market segment) won't be interested since they are going fully custom and I doubt that an LGA socket will work with their on-package custom-build wide RAM interfaces. So in the end we are left with things like Dell XPS 13, MS Surface and few others. These are all popular and impactful brands, but they are just a drop in the bucket compared to the total PC sales. And I doubt that technology reserved to only selected premium laptops is going to be cheap.
    - deleted 5y ago
      [deleted]
    - Brakenshire 5y ago
      If LPDDR is faster won’t desktops and gaming laptops also want it? One possible other compromise could be soldered LPDDR RAM, but with a DIMM expansion slot for DDR as well. I wonder whether the DDR could be switched off and the baseline power draw eliminated if the RAM usage was below needing it.
      - baybal2 5y ago
        > If LPDDR is faster won’t desktops and gaming laptops also want it? The desktop version of LPDDR4 is there, it's just called DDR5.
      - eropple 5y ago
        So I will preface this with that I'm not an expert. But as I understand it, multicore systems are already frequently NUMA, but to a degree that most stuff (I am eliding categories of code here, but you get the idea) don't have to really care. From my understanding of how all this works, the difference of speed and bandwidth for LPDDR versus DDR seems like risking significant complexity for an expandability that few people would use and in turn cause an everything-or-nothing problem, where either high-performance code is written assuming anybody might have this, or nobody assumes it and you get a pile of stalls.
- deleted 5y ago
  [deleted]
- jdsully 5y ago
  You can't compare balls on the BGA package to signal pins. The vast majority of these are for power and ground. LPDDR4 actually has fewer data lines than DDR4.
- PicassoCTs 5y ago
  We have cpus with lots of pins, nobody is stopping ram from switching to a cpu socket layout..
  - emteycz 5y ago
    Laptop CPU is onboard for the same reasons RAM is. This is not about the amount of pins, it's about power requirements for signal clarity.
wayoutthere 5y ago
There’s no technical reason not to (I’m no EE but I’m sure it could be done somehow), but there’s no demand for removable memory. The entire consumer PC market is already a rounding error for the semiconductor industry, and the enthusiast market that would be interested in this is a very small portion of that market. Like it or not, repairable/upgradable laptops are a thing of the past. There’s just not component support or sufficient market demand to make the parts removable anymore.
- vimacs2 5y ago
  Way overstating your case. PC's might be on the decline but they are still far far from being a "rounding error for the semiconductor industry". Laptops also make up a major component of that still very alive market so no, I disagree that there is not enough market demand for having laptops that can be repaired or upgraded. It's the industry themselves that have worked to hamper the right of repair while giving nebulous pseudo-technical rationalizations for it.
  - wayoutthere 5y ago
    Modern laptop motherboards can easily be about the size of a cell phone. Most of the case is battery and the main board is a shrinking percentage of the BOM cost. The entire motherboard is the replaceable component. It’s less “right to repair” than the additional components and design required to make them repairable are more expensive than just replacing the whole board.
    - vimacs2 5y ago
      Seems like a deliberate design choice, not some inevitable consequence of modernity. Why exactly does the board need to be cell phone sized when the actual form factor of even a netbook is substantially larger?
      - dhosek 5y ago
        To fit more battery. Other than my Mac mini, every computing device (including watch and phone) I own is mostly battery inside.
mumblemumble 5y ago
I've never done anything beyond amateur electronics, so sorry if I'm way off base here, but it at least seems intuitively plausible to me that soldering the components to the board allows them to work reliably at lower power. With a pin and socket connection, you've got to try and be at least reasonably resistant to corrosion or other sources of less-than-perfect connection. That said, I don't know that RAM chips are the hill I want to die on, anyway. Could we get to a better place if we dispensed with the whole, "just the one big motherboard," design, and looked to the old backplane-style physical layouts? Then you could have a module that contains the CPU and RAM and suchlike all in a single package, and move other things that may not want to be quite as tightly integrated off to another package.
- mikepurvis 5y ago
  Up until relatively recently, a lot of laptops and even phones would put the connectors on separate PCBs connected by a ribbon, so that damaging those wouldn't mean a $500 motherboard replacement. I definitely remember ordering a replacement headphone socket board for an old MacBook and just putting it in myself, and I've done similar with, eg, the connector port board on a PS4 controller. But I guess this is one of the hazards of Apple having their AppleCare programme— they can do the math and calculate that saving a dollar on the cost of making and mounting and connecting that extra component still makes them money even if they have to eat the occasional full motherboard in the first three years of ownership.
  - ribit 5y ago
    If I am not mistaken the ports on recent Apple machines are on a separate, easily replaceable board.
    - sgerenser 5y ago
      Doesn’t appear to be the case on the 16” MBP: https://www.ifixit.com/Teardown/MacBook+Pro+16-Inch+2019+Teardown/128106 https://www.ifixit.com/Teardown/MacBook+Pro+16-Inch+2019+Tea...
nrp 5y ago
ribit and others are correct. While this may have been possible in the past, at modern memory frequencies and timings, it's not really plausible to deviate from what the platforms are designed for: LPDDR being soldered and placed a specific layout area relative to the CPU, and for socketed DDR, the sockets being placed in one of a few placements relative to the CPU, with a little layout wiggle room. Edit: I guess to clarify, the plausibility challenge is that whether or not it is theoretically possible, the platform owner (Intel, AMD, etc) or the memory vendors (Samsung, SK Hynix, Micron) are unlikely to support the lark.

by tomxor 5y ago

baybal2 5y ago

Yes, as I wrote somewhere below, LPDDR4 signal is actually more robust than DDR4 signal, and LPDDR4 controllers have more features to fix degraded signals. DDR5 has more roots in the LPDDR4 than in the regular DDR4.

ribit 5y ago

LPDDR is low power because it is a more sophisticated device with more complex protocol compared to regular DDR, because it has a higher pinout allowing it to have a more efficient electrical connection and because the computer manufacturer can optimize the connection with specific chips in mind instead of having to support a wide range of devices. I think the number of pins is a practical limitation. Current DDR DIMMs use 260-280 pins if I remember correctly, while an average LPDDR4X BGA package is 400 balls or higher. Apple uses chips with 877 balls. It is definitely possible to design modular RAM with high-pinout, but would it be economically feasible?

rthomas6 5y ago
It is if it's a standard that everyone decides to support...
- ribit 5y ago
  That's the thing, who is everyone? Such technology would only be relevant to premium-level ultraportable notebooks. Desktops, gaming laptops as well as budget laptops would stick with the cheaper and more ubiquitous DDR. Smartphones and tables will continue to solder RAM on due to space constraints. Apple (who is the driving force in this market segment) won't be interested since they are going fully custom and I doubt that an LGA socket will work with their on-package custom-build wide RAM interfaces. So in the end we are left with things like Dell XPS 13, MS Surface and few others. These are all popular and impactful brands, but they are just a drop in the bucket compared to the total PC sales. And I doubt that technology reserved to only selected premium laptops is going to be cheap.
  - deleted 5y ago
    [deleted]
  - Brakenshire 5y ago
    If LPDDR is faster won’t desktops and gaming laptops also want it? One possible other compromise could be soldered LPDDR RAM, but with a DIMM expansion slot for DDR as well. I wonder whether the DDR could be switched off and the baseline power draw eliminated if the RAM usage was below needing it.
    - baybal2 5y ago
      > If LPDDR is faster won’t desktops and gaming laptops also want it? The desktop version of LPDDR4 is there, it's just called DDR5.
    - eropple 5y ago
      So I will preface this with that I'm not an expert. But as I understand it, multicore systems are already frequently NUMA, but to a degree that most stuff (I am eliding categories of code here, but you get the idea) don't have to really care. From my understanding of how all this works, the difference of speed and bandwidth for LPDDR versus DDR seems like risking significant complexity for an expandability that few people would use and in turn cause an everything-or-nothing problem, where either high-performance code is written assuming anybody might have this, or nobody assumes it and you get a pile of stalls.
deleted 5y ago
[deleted]
jdsully 5y ago
You can't compare balls on the BGA package to signal pins. The vast majority of these are for power and ground. LPDDR4 actually has fewer data lines than DDR4.
PicassoCTs 5y ago
We have cpus with lots of pins, nobody is stopping ram from switching to a cpu socket layout..
- emteycz 5y ago
  Laptop CPU is onboard for the same reasons RAM is. This is not about the amount of pins, it's about power requirements for signal clarity.

wayoutthere 5y ago

There’s no technical reason not to (I’m no EE but I’m sure it could be done somehow), but there’s no demand for removable memory. The entire consumer PC market is already a rounding error for the semiconductor industry, and the enthusiast market that would be interested in this is a very small portion of that market. Like it or not, repairable/upgradable laptops are a thing of the past. There’s just not component support or sufficient market demand to make the parts removable anymore.

vimacs2 5y ago
Way overstating your case. PC's might be on the decline but they are still far far from being a "rounding error for the semiconductor industry". Laptops also make up a major component of that still very alive market so no, I disagree that there is not enough market demand for having laptops that can be repaired or upgraded. It's the industry themselves that have worked to hamper the right of repair while giving nebulous pseudo-technical rationalizations for it.
- wayoutthere 5y ago
  Modern laptop motherboards can easily be about the size of a cell phone. Most of the case is battery and the main board is a shrinking percentage of the BOM cost. The entire motherboard is the replaceable component. It’s less “right to repair” than the additional components and design required to make them repairable are more expensive than just replacing the whole board.
  - vimacs2 5y ago
    Seems like a deliberate design choice, not some inevitable consequence of modernity. Why exactly does the board need to be cell phone sized when the actual form factor of even a netbook is substantially larger?
    - dhosek 5y ago
      To fit more battery. Other than my Mac mini, every computing device (including watch and phone) I own is mostly battery inside.

mumblemumble 5y ago

I've never done anything beyond amateur electronics, so sorry if I'm way off base here, but it at least seems intuitively plausible to me that soldering the components to the board allows them to work reliably at lower power. With a pin and socket connection, you've got to try and be at least reasonably resistant to corrosion or other sources of less-than-perfect connection. That said, I don't know that RAM chips are the hill I want to die on, anyway. Could we get to a better place if we dispensed with the whole, "just the one big motherboard," design, and looked to the old backplane-style physical layouts? Then you could have a module that contains the CPU and RAM and suchlike all in a single package, and move other things that may not want to be quite as tightly integrated off to another package.

mikepurvis 5y ago
Up until relatively recently, a lot of laptops and even phones would put the connectors on separate PCBs connected by a ribbon, so that damaging those wouldn't mean a $500 motherboard replacement. I definitely remember ordering a replacement headphone socket board for an old MacBook and just putting it in myself, and I've done similar with, eg, the connector port board on a PS4 controller. But I guess this is one of the hazards of Apple having their AppleCare programme— they can do the math and calculate that saving a dollar on the cost of making and mounting and connecting that extra component still makes them money even if they have to eat the occasional full motherboard in the first three years of ownership.
- ribit 5y ago
  If I am not mistaken the ports on recent Apple machines are on a separate, easily replaceable board.
  - sgerenser 5y ago
    Doesn’t appear to be the case on the 16” MBP: https://www.ifixit.com/Teardown/MacBook+Pro+16-Inch+2019+Teardown/128106 https://www.ifixit.com/Teardown/MacBook+Pro+16-Inch+2019+Tea...

nrp 5y ago

ribit and others are correct. While this may have been possible in the past, at modern memory frequencies and timings, it's not really plausible to deviate from what the platforms are designed for: LPDDR being soldered and placed a specific layout area relative to the CPU, and for socketed DDR, the sockets being placed in one of a few placements relative to the CPU, with a little layout wiggle room. Edit: I guess to clarify, the plausibility challenge is that whether or not it is theoretically possible, the platform owner (Intel, AMD, etc) or the memory vendors (Samsung, SK Hynix, Micron) are unlikely to support the lark.