Why the MacBook Pro is limited to 16GB of RAM

It wouldn’t be a new product without praise and criticism, this usually comes in at least a slightly positive balance. Although for the new MacBook Pro Devices Apple announced on 27th October the outcry has been louder and stronger than the usual grumblings.

There were many areas that professional users found cause for concern, some disliked the new USB-C ports, some critiqued the lack of new Kaby lake processors – but the most vitriol has been towards the limiting of RAM to 16gb. Many claiming this is a huge disappointment and the MacBook Pro now wont provide them with their use case. Well whether you agree with the reasoning or not, there is a good reason behind it.


Why the MacBook Pro is limited to 16GB of RAM

Phil Schiller was quick to come out and calm the initial dissatisfaction behind the apparent lack of RAM. In an email response to an Apple customer passed on to 9to5Mac, Phill put the reasoning down to battery life.

To put more than 16GB of fast RAM into a notebook design at this time would require a memory system that consumes much more power and wouldn’t be efficient enough for a notebook. I hope you check out this new generation MacBook Pro, it really is an incredible system. – Phil Schiller

RAM and battery life

With Intel only just launching Kaby lake processors, being behind the time frame needed for Apple to work on integration into the MacBook Pro and MacOS. Apple had no option but to use Intel’s 6th Generation chipset which supports DDR3 RAM, Low Power DDR3 RAM (LPDDR), and DDR4 RAM. Unfortunately they do not support LPDDR4 or DDR4L (the low power version), opting for more than 16GB would mean using DDR4 RAM and using more power.

So Apple had no choice but to opt for a maximum of 16gb of RAM in LPDDR3E which runs at 1855Mhz. How much power exactly is being saved by opting for LPDDR3E?

MacDaddy had a look into the power usage of the RAM variations. Under normal conditions LPDDR3E uses 1.5 watts whereas DDR4 would use about 3-5 watts. Meaning about 20% of the overall system power would be allocated to running DDR4 compared to less than 10% for LPDDR.

Why the MacBook Pro is limited to 16GB of RAM

The DDR4 figures are taken from a PC as apposed to a MacBook Pro or indeed a MacOS machine, so Apple may be able to improve these figures. The difference in power difference is hotly contested, with some claiming large benefits and some results showing negligible difference between DDR3 and DDR4. However figures seem to show 2 and 5 watts are saved using LPDDR3E RAM instead of DDR4.

RAM and the use case

So the figures are certainly up for debate and the increase in power could be negligible. However background power usage of DDR4 ram is much higher than the lower power option used. As much as 200% power usage can be seen in wasted energy in returning to sleep mode once RAM has been used.

“The DDR4 background energy is a big contributor to the overall DDR4 energy due to the lack of a fast power down mode, which offsets the IO energy savings” – http://www.cs.rochester.edu/~ipek/micro15.pdf (pdf)

Also take into account sleeping with LDDPR RAM is much more efficient. As much as 80% less energy intact, so these are numbers that simply cannot be ignored. Something that is obvious considering DDR is developed for devices that are plugged in, where as LPDDR is for mobile devices that are in and out of sleep quite a lot.

Why the MacBook Pro is limited to 16GB of RAM

Switching to the supported DDR4 ram, which is the only option to install more that 16gb would decreased the 30days average standby time to less than a week. This might not be in your usage, but it helps quite a bit when considering you are using a laptop. Next time you open the lid and the battery is at 50%, that would be completely depleted if Apple had chosen different RAM.

Apple would have adopted LPDDR4 RAM should the Intel chips have supported it. This is obvious given the fact the iPhone 7 already uses it, along with Apples ARM architecture CPU. So when Apple claim battery life is the reason, it really is.

Slimming the MacBook Pro

With that all said, there is another issue at hand here, and that’s Apples pursuit for thinness. The volume of space inside the MacBook is the most limiting factor of battery life, and although Apple work hard to squeeze life from the cells they are hindering life dramatically.

Why the MacBook Pro is limited to 16GB of RAM

Apple commenters such as Rene Ritchie are always quick to blame rules and regulations for the lack of volume. With the iPad pro, this maybe the case, but Apple could have put a 24% larger battery in the new MacBook Pro and still been inside limits imposed by the Federal Aviation Administration. Although this still won’t have upped battery life on a DDR4 machine to the levels of their LPDDR version.

Apple without doubt could have put more battery inside to aid in the lacklustre battery life users are reporting. However opting for more RAM as an option would have reduced this even more. The limiting RAM will not suit users that are rendering video or anything intensive in the slightest, so perhaps right now its time to look at other options. However when Apple make decisions it usually for a good reason – although you might not like it.

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