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My Mac (Mid 2009- MacBookPro5,5) installing OS 10.8.2.

Currently, it is using 2 x 1GB (1066 Mhz).

My friend gave me 2 x 2GB (1600 Mhz) of his 2012 Mac.

After installing 2 x 2GB (1600 Mhz) on my Mac, it can not boot but can not start OS. This is the error that show on boot start up screen:

enter image description here

But it is possible to install 1x 1GB (1066) + 1x 2GB (1600). The system can down-clock it to both 1066 Mhz. But what i still have 1 x 1GB (1066) + 1x 2GB (1600) left!

3GB @ 1066 Mhz

My question is: Any better solution than using 1x 1GB (1066) + 1x 2GB (1600)? More certainly, is there any way to install 2 x 1600 Mhz? (even down-clocking to 1066 is accepted).

Edit 1: 4 RAM are healthy.

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Are you 100% sure the model you have supports more then 3GB of system memory? Are you 100% the memory your trying to use is not actually defective? Are you 100% was is likely the 32-bit OS X kernel can support more then 3GB? I am going to take a very educated guess based on 15 years of solving problems like this, the problem simply is, your motherboard does not support a 2GBx2 configuration( not much you can do about that fact ). – Ramhound Jan 30 '13 at 18:17
    
@Ramhound No, that Macbook Pro model should definitely support 2Gbx2. – Marcus Chan Jan 30 '13 at 18:39
1  
@BachT Try booting off of each of the 2 RAM modules your friend gave you separately, and if they both boot sucessfully, try running a memory check on them with Apple Hardware Test on your OS CD. I'm betting one of them has an error. – Marcus Chan Jan 30 '13 at 18:42
    
@MarcusChan: all of them are healthy. I removed each of them and plug it with a 1-GB-1066 Mhz and it work well. But both of 1600 can not start my system. – BachT Jan 30 '13 at 20:05
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@BachT - Of course both of them being at 1600 won't boot your system. You will have to set the frequency youself ( if the BIOS allows you to do that ) or use the correct memory frequency. The reason a single stick works is because of the nature of DDR3 memory. – Ramhound Jan 30 '13 at 20:45

Despite this thread being very old, I am answering this, so users will have a fair idea of this model's memory compatibility.

This MacBook Pro variant will support up to 8 GB. DDR3 1066 MHz is the safest and compatible speed. Anything more than that speed is overkill. While a single 1 GB 1600 MHz may work, 2 GB's or 4 GB's with 1600 MHz will not work.

Two different speeds will default the whole memory system to the lowest speed. 1066 MHz + 1600 MHz will run at 1066 MHz - Automated Down-clocking by the system.

And the only other way to down-clock would be to use a Windows environment, edit the speed and back to Macintosh OS.

Refer this solution

Good luck!

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