Take the 2-minute tour ×
Ask Different is a question and answer site for power users of Apple hardware and software. It's 100% free, no registration required.

This question already has an answer here:

Can MacBook Pro's successfully support and fully exploit RAM of a higher MHz rating than that which they ship with?


For example, take my 15" MacBook Pro (Late 2011) that ships with 4GB of 1333MHz DDR3 memory. I'm considering buying 16GB of the same clock speed even though Apple says that it can "support up to 8GB" — but we know that Apple is wrong.

What about installing 1600MHz in the 16GB variant — will it work? Or will it be clocked down to 1333MHz? When compared to 16GB 1333MHz, will the higher clock speed improve battery life, performance, timings, or what?

share|improve this question

marked as duplicate by patrix Jun 17 '13 at 16:38

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
@FLY, the answers there aren't great... –  Baumr Jun 17 '13 at 14:11
    
Would you edit the text of this to make it explicitly clear how this is different than the linked question? Perhaps you could document that "support" and "exploit" mean technically or remove them if they are noise. –  bmike Aug 5 '13 at 11:33

2 Answers 2

The processor is hardwired to talk to the memory so it will throttle memory down to the speed it can talk at.

Installing 1600MHz RAM will just run at 1333MHz in that model MacBook Pro. There is no impact on battery life, performance, reliability etc.

I know there was an issue on some models where it would not boot with 2 modules of higher speed but I believe it is fine with the new models. There are utilities you can get to change the memory speed (on some modules) to get around this issue. I am not sure if this is the case with newer models.

The last time, I looked the price difference between these speeds of RAM was so small, I would just get the 1333 models for safety.

(MHz = clock speed)

share|improve this answer
    
Thanks! But what do you mean about the price difference? If there was no different and both were compatible, then the faster one would surely be the better choice just in case it does make something faster, etc. (I'm not arguing in favor of this statement, just playing devil's advocate) –  Baumr Dec 3 '12 at 15:57
2  
What I mean was for total safety, I would buy the 1333 ram unless the 1600 is way cheaper. You will not get any benefit from the faster ram and there is a very small chance that 1600 may not work. If the place you are buying from will accept returns, then get the 1600 and if does not work 100%, just return it and get the 1333. –  Alain King Dec 4 '12 at 7:39
2  
As I said in my previous statement, get the 1600MHz and try it. If the Mac is reporting 1600 then it is running at 1600, just be aware that some comments on the threads you added do talk about instability. I know apple says there is a limit in ram that is not always true. I am typing this on an imac with 20gb of ram where there is a maximum of 16 according to apple. –  Alain King Dec 13 '12 at 7:37
2  
@AlainKing – I think with the Core-i processors and especially the Intel chipsets the Memory Bus speed is no longer locked, as it used to be with the NVIDIA chipsets. That is, if you use 1600 MHz RAM is is actually recognized and run at 1600 MHz (or should be). –  iolsmit Dec 16 '12 at 10:55
up vote 3 down vote accepted

The short answer is that it will depend on the model of your machine, and the RAM manufacturer you buy from — but I can't tell you any specifics on either.

Installing higher MHz RAM is a risk, and here's why:


My 1600 MHz memory didn't pass tests

I installed 1600 MHz RAM on my laptop and found that it failed the Apple Hardware Test, Memtest OS X, and the Tech Tool Pro memory tests.

These could have simply been faulty RAM modules, or just not 100% compatible with my machine.

So follow the advice below at your own risk.


"But it's compatible with my Intel processor"

Here's what I've found:

  • Intel's spec for my i7 processor (2760QM on a Late 2011 MacBook Pro) says that 1600 MHz DDR3 RAM is compatible.

But does that translate for Macs? Yes according to OWC.

However, Macs are notoriously picky about RAM, and while 1600 MHz memory might be compatible with Intel, it doesn't meant it'll be compatible with the Apple logic board.

So find out if Intel supports it, but that is no guarantee.


Costs of 1600 vs. 1333 MHz

If the decision between two MHz-ratings of RAM comes down to price, take a look at the real-world performance increase and judge whether it's worth it.

It's likely that it may not be worth it to get the "faster" memory.

Also take into account the risks if it doesn't work: you'll have to return it (if even possible).


Is this a false positive?

Some people allege in various places that 1600 MHz will work because it shows up in "About this Mac" when installed:

enter image description here

And then "More Info" brings this up:

enter image description here

First, there is the question of whether it will pass memory tests (see the first section).

Also, I am unsure on how one can test if it is not being clocked down to 1333 MHz and the full 1600MHz are being used.

I am not sure whether showing up there means it works.

share|improve this answer
    
Mine shows 1333 MHz, so I guess if it shows 1600 MHz it's a good sign that it actually runs at higher speed. –  iolsmit Dec 16 '12 at 10:52

Not the answer you're looking for? Browse other questions tagged or ask your own question.