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How much more work would it be to put in more RAM that could only be used when plugged into AC power? My understanding of the MacBook Pro design constraint is t

How much more work would it be to put in more RAM that could only be used when plugged into AC power? My understanding of the MacBook Pro design constraint is that they had to hit <100 watt-hours while using LPDDR3. Could a laptop easily have another 16 or 32 GB of RAM that consumes more power but is only available when plugged into AC power? I would be happy to have such a constraint. I love my MacBook Pro. I love being able to carry it around and deal with things like email when on battery. When I'm doing serious development work, I'm sitting down somewhere plugged in anyhow. The OS could gracefully page out to swap and power down the less efficient memory when switched to battery.

cududa 10y ago
Seems like a lot of engineering work for something that'll be solved around the end of the year
- mcculley 10y ago
  I agree with that in this particular case. I would imagine the next rev of the MacBook Pro will use some Intel chipset that can support LPDDR4 or something. But I'm wondering about this in the general case. For some definitions of "power user", it would make sense for the system to behave differently when running on battery. Pushing these design decisions down into hardware is something Apple does better than others, as they control the whole stack.
pimlottc 10y ago
Are there any existing operating systems that can handle a dynamically-changing amount of RAM? > The OS could gracefully page out to swap and power down the less efficient memory when switched to battery. According to benchmarks, the SSD on the latest MacBook Pro hit 1.4GB/s. Even at this speed, it would take at least 10 seconds to flush 16GB of RAM to disk. I doubt your computer could do much while that was happening. I wouldn't call that very graceful.
- mcculley 10y ago
  > Are there any existing operating systems that can handle a dynamically-changing amount of RAM? Some implementations of Linux do this on exotic hardware (NUMA). > Even at this speed, it would take at least 10 seconds to flush 16GB of RAM to disk. It needn't happen atomically.
- rrdharan 10y ago
  Solaris on SPARC had the ability to dynamically add or remove RAM as I understand it. I believe IBM AIX (+ POWER maybe?) can do this too. Modern Linux kernels will let you hot-add memory but won't let you hot remove it.
  - scurvy 10y ago
    Yep, CPU's too. On the E4500's the CPU's and memory were on the same boards. You could remove the board after sending the right ASR commands. Then again, you were constantly swapping boards to find the ones not affected by EDP (ecache data parity) errors.
  - throwaway7767 10y ago
    Some x86 boards have hot-pluggable memory too (it's a ACPI feature), it's been a very long time since that was a big-iron-only feature.
- nullc 10y ago
  Ram hotplug is a standard linux kernel feature (obviously one that requires hardware support...)

cududa 10y ago

Seems like a lot of engineering work for something that'll be solved around the end of the year

mcculley 10y ago
I agree with that in this particular case. I would imagine the next rev of the MacBook Pro will use some Intel chipset that can support LPDDR4 or something. But I'm wondering about this in the general case. For some definitions of "power user", it would make sense for the system to behave differently when running on battery. Pushing these design decisions down into hardware is something Apple does better than others, as they control the whole stack.

pimlottc 10y ago

Are there any existing operating systems that can handle a dynamically-changing amount of RAM? > The OS could gracefully page out to swap and power down the less efficient memory when switched to battery. According to benchmarks, the SSD on the latest MacBook Pro hit 1.4GB/s. Even at this speed, it would take at least 10 seconds to flush 16GB of RAM to disk. I doubt your computer could do much while that was happening. I wouldn't call that very graceful.

mcculley 10y ago
> Are there any existing operating systems that can handle a dynamically-changing amount of RAM? Some implementations of Linux do this on exotic hardware (NUMA). > Even at this speed, it would take at least 10 seconds to flush 16GB of RAM to disk. It needn't happen atomically.
rrdharan 10y ago
Solaris on SPARC had the ability to dynamically add or remove RAM as I understand it. I believe IBM AIX (+ POWER maybe?) can do this too. Modern Linux kernels will let you hot-add memory but won't let you hot remove it.
- scurvy 10y ago
  Yep, CPU's too. On the E4500's the CPU's and memory were on the same boards. You could remove the board after sending the right ASR commands. Then again, you were constantly swapping boards to find the ones not affected by EDP (ecache data parity) errors.
- throwaway7767 10y ago
  Some x86 boards have hot-pluggable memory too (it's a ACPI feature), it's been a very long time since that was a big-iron-only feature.
nullc 10y ago
Ram hotplug is a standard linux kernel feature (obviously one that requires hardware support...)