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sir.riel

macrumors member
Original poster
Apr 29, 2015
41
0
Cambodia
Hi I just recently picked up a mid 2015 15" MBP and noticed that the ram speed is still at 1600mhz, the same as my old mid 2012. Looking up specs for the 13" mbp, it has 1866mhz ram

why the difference in speed? spec wise shouldn't the 15" have the faster speed ram?
 

sentential

macrumors regular
May 27, 2015
169
72
Ram speed for the core series is negligible you'll see minimal gains because ram throughput isn't just about speed but a combination of speed and timing. Higher speed RAM often has higher latency and as a result performs the same as slower speed RAM. It has more to do with the manufacturer of the RAM itself rather than one being faster than another. Think of it more along the lines of tech vs horsepower. Just because one is a pushrod,flat,v-config,iron block doesn't matter per say when they all put out the same horsepower. Its just about how you get there, for example

1-1-1-10 @ 100mhz
2-2-2-10 @ 200mhz

Are essentially the same in terms of throughput so:

10-11-10-30 @ 1866
9-9-9-24 @ 1600
= about 10% difference in latency so the 1600 is actually ~1760mhz effective so the 1866 is faster but not by much. See?

TLDR: The difference you're seeing is because the 15" use the 4th gen Crystalwell and the 13" uses 5th Broadwell. They are both roughly about the same the only difference is that BW is a die shrink of CW to save power so the RAM is different as a result.
 
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T5BRICK

macrumors G3
Aug 3, 2006
8,313
2,387
Oregon
As sentential said, you won't notice a difference.

And to elaborate on what was already stated, the maximum memory speed is determined by the memory controller, which is integrated into the CPU on recent Intel processors. The newer CPUs on the 13" rMBPs can run faster memory.
 
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