Last week, we found out that Apple’s new MacBook Pros would be limited to a maximum of 16GB of RAM.
As we reported on Friday, Apple said that they decided against giving the 32GB option because doing so would have consumed more energy causing battery life to decrease. Even though the statement from Apple is true, it lacks a lot of detail.
The Loop’s Dave Mark, in addition to comments from a Reddit user, point us to a slightly more detailed explanation for why you can’t outfit your new MacBook Pro with 32GB of RAM. Mark blames the lack of a larger memory configuration on Intel’s Skylake chip’s lack of LPDDR4 support. LPDDR4 (LP stands for low power) is the latest standard for low-voltage RAM.
Let’s expand on this and investigate a bit more. Intel won’t offer official support for LPDDR4 memory until their Kaby Lake line of CPUs, which were announced on August 30, start shipping later this year. Apple’s new MacBook Pros shipped with Intel’s Skylake processors and LPDDR3 RAM. Intel’s Skylake processors support DDR4 and LPDDR3.
Both DDR4 and LPDDR3 run at 1.2V, while LPDDR4 runs at 1.1V. Given that both DDR4 and LPDDR3 run at the same voltage, Apple could have used 32GB of DDR4 memory with an increase in energy consumption. However, the DDR4 version of memory will run at a higher clock speed, which will lead to greater energy consumption as more bits need to be pushed around at any given time.
The new MacBook Pro already uses a faster SSD, which occupies more bandwidth on the PCI-e bus. If you add RAM with an even higher clock speed, you can cause bottlenecks on the system bus, which would put a higher energy strain on the system. As you add more RAM to the system, the CPU has to do more work as well to index and search content stored in memory. All of these are factors that lead Apple ultimately to choose a 16GB limit for the RAM.
With Apple’s memory constraints, the new MacBook Pro can deliver all-day battery life, with up to 10 hours or browsing or movie playback on both 13 and 15-inch models.