Developer Ben Slaney did a thorough look at why Apple’s latest MacBook Pros are limited to 16GB. The answer? The type of low-power RAM they use provides a significant reduction in power consumption:
It’s impossible to get an exact figure on it, but depending on the usage it can be estimated that between 2 and 5 watts are saved using LPDDR3E RAM instead of DDR4. And since the system averages to drawing about 20 watts on battery in normal usage, this can be said to be the difference of the RAM using 2 watts versus 3-6 watts for DDR4. Translated to overall power usage that would make the difference of 10% of power being dedicated to RAM versus the 20-30% it would be for DDR4.
That low power RAM standard maxes out at 16GB. Long story short: to go to 32GB, Apple would have to jump to desktop-class DDR4 RAM, which would eat up a lot more juice. Slaney also got a message from Apple’s Phil Schiller, who also confirmed that 32GB of RAM would have necessitated a different logic board design.
It seems unlikely that MacBook Pros will be stuck at 16GB forever. Slaney says that Intel’s current architecture doesn’t yet support the next generation of low power RAM, which suggests one interesting potential course:
Apple have never made big compromises in their engineering, and to switch to DDR4 memory now just to support 32GB would be relatively absurd given the disadvantages which are outlined in this article. They would be more likely to replace the Intel CPU with their in-house manufactured ARM CPU in order to support LPDDR4.
Apple’s already had some frustrations with Intel’s processor advancement and scheduling over the last couple years; this is just another. At some point, Cupertino’s going to hit that last straw.