6 ms·

Can you please point us to some technical report or something where they document the energy saving of moving from dimm slots to soldered ram/ssd ?

ribit 5y ago
Unfortunately, I am not aware of any document like that. There are some papers comparing everything efficiency of different types of RAM, and there is of course indirect evidence of premium notebooks having significantly improved the battery life after moving to LPDDR.
- formerly_proven 5y ago
  LPDDR does many, many things to reduce power consumption (the current version even does DVFS, which I think is a first for main memory; graphics cards have been doing interface DFS for a long time, but a high end graphics card will burn around 30-70 W in the memory chips, and uses extremely high speed PHYs running at around 20 GBit/s per pin in the current generation). The only thing that really changes between DIMM and soldered on is a somewhat increased trace length. That accounts only for a very small increase in power.
  - foldr 5y ago
    > That accounts only for a very small increase in power. What are you basing this statement on?
    - formerly_proven 5y ago
      PHY is only part of the DRAM chip, and trace length is only a part of what determines energy per bit, so increasing trace length by x % wouldn't increase overall power by x %, but a fraction of that. Thinking about it, there is a bigger problem than just energy/bit scaling; since LPDDR switches dynamically between high-speed and lower speed modes, the high speed mode is likely not used a lot. However, the low speed modes rely on being able to turn the termination off, which saves significant amounts of power. A socket may make that difficult to achieve, and if you have to run with ODT in the, I'm assuming, mostly-used low power mode, you might end up with a significant increase in power.
      - foldr 5y ago
        Of course there are multiple factors at play, but that observation doesn’t justify the conclusion that any particular factor makes only a ‘very small l’ contribution. Do you have even a back-of-an-envelope calculation to support this claim? The knock-on effects of increased trace length can be quite complex.
franga2000 5y ago
I don't think you'll find any. The way I understand it, the savings come from the new LP variant of DDR chips and nobody ever bothered to put them on DIMMs. And even if the DIMM design (it's more than just a slot) doesn't make sense anymore, we could easily make a new "dumb" memory slot standard that would allow us to swap out the chips directly - like we have for CPUs.
- foldr 5y ago
  > we could easily make a new "dumb" memory slot standard that would allow us to swap out the chips directly - like we have for CPUs. You could, but it would take up a lot of space, given the higher pin count, and would most likely increase power consumption.
ribit 5y ago
By the way, check out reviews of the Framework Laptop for a first-hand illustration of this effect. They seem to be getting 40-50% lower battery runtimes than laptops with comparable specs. That's example the problem — of you design for modularity, you have to leave some optimizations on the table.
- nrp 5y ago
  The battery impact for us at this point is likely more a factor of additional firmware and driver tuning that we need to do. We've tested to 10-11 hours in MobileMark 2018, but have actually seen video playback runtime (which should be a lighter load) drop below that due to some audio driver issues that we're working through. There is certainly some impact to using DDR4 instead of LPDDR4, but we believe it is still the better choice for most consumers by allowing for greater product longevity at lower cost.
  - collinmanderson 5y ago
    How about standby time?
- formerly_proven 5y ago
  Doubtful, the Framework laptop is pretty much like any other USB-C-based laptop, except that it reserves some space inside the chassis so that the adapter dongles are flush with the case.
- michaelmrose 5y ago
  That doesn't in any way tease out the effects of sockets it seems impossible that that doubles power usage.

ribit 5y ago

Unfortunately, I am not aware of any document like that. There are some papers comparing everything efficiency of different types of RAM, and there is of course indirect evidence of premium notebooks having significantly improved the battery life after moving to LPDDR.

formerly_proven 5y ago
LPDDR does many, many things to reduce power consumption (the current version even does DVFS, which I think is a first for main memory; graphics cards have been doing interface DFS for a long time, but a high end graphics card will burn around 30-70 W in the memory chips, and uses extremely high speed PHYs running at around 20 GBit/s per pin in the current generation). The only thing that really changes between DIMM and soldered on is a somewhat increased trace length. That accounts only for a very small increase in power.
- foldr 5y ago
  > That accounts only for a very small increase in power. What are you basing this statement on?
  - formerly_proven 5y ago
    PHY is only part of the DRAM chip, and trace length is only a part of what determines energy per bit, so increasing trace length by x % wouldn't increase overall power by x %, but a fraction of that. Thinking about it, there is a bigger problem than just energy/bit scaling; since LPDDR switches dynamically between high-speed and lower speed modes, the high speed mode is likely not used a lot. However, the low speed modes rely on being able to turn the termination off, which saves significant amounts of power. A socket may make that difficult to achieve, and if you have to run with ODT in the, I'm assuming, mostly-used low power mode, you might end up with a significant increase in power.
    - foldr 5y ago
      Of course there are multiple factors at play, but that observation doesn’t justify the conclusion that any particular factor makes only a ‘very small l’ contribution. Do you have even a back-of-an-envelope calculation to support this claim? The knock-on effects of increased trace length can be quite complex.

franga2000 5y ago

I don't think you'll find any. The way I understand it, the savings come from the new LP variant of DDR chips and nobody ever bothered to put them on DIMMs. And even if the DIMM design (it's more than just a slot) doesn't make sense anymore, we could easily make a new "dumb" memory slot standard that would allow us to swap out the chips directly - like we have for CPUs.

foldr 5y ago
> we could easily make a new "dumb" memory slot standard that would allow us to swap out the chips directly - like we have for CPUs. You could, but it would take up a lot of space, given the higher pin count, and would most likely increase power consumption.

ribit 5y ago

By the way, check out reviews of the Framework Laptop for a first-hand illustration of this effect. They seem to be getting 40-50% lower battery runtimes than laptops with comparable specs. That's example the problem — of you design for modularity, you have to leave some optimizations on the table.

nrp 5y ago
The battery impact for us at this point is likely more a factor of additional firmware and driver tuning that we need to do. We've tested to 10-11 hours in MobileMark 2018, but have actually seen video playback runtime (which should be a lighter load) drop below that due to some audio driver issues that we're working through. There is certainly some impact to using DDR4 instead of LPDDR4, but we believe it is still the better choice for most consumers by allowing for greater product longevity at lower cost.
- collinmanderson 5y ago
  How about standby time?
formerly_proven 5y ago
Doubtful, the Framework laptop is pretty much like any other USB-C-based laptop, except that it reserves some space inside the chassis so that the adapter dongles are flush with the case.
michaelmrose 5y ago
That doesn't in any way tease out the effects of sockets it seems impossible that that doubles power usage.