MacBook – What are the consequences of using DDR3 RAM in DDR2 MBP4.2

This is down to a limitation in some memory controllers and how they handle memory sticks with different memory characteristics (also add into the fact that you have no control over these settings in EFI as you might have in a non-EFI BIOS)

When you put both new sticks in, the memory controller is trying to set up the memory according to the specs advised by the PNY SODIMMs, however it is having problems with that configuration and fails to initialise the memory.

When you put in a stick of the older RAM, it changes the configuration to use the slower RAM's settings and the second stick of RAM is actually running at the slower speeds and timings of the old RAM and these are invariably "slower" and more conservative than those the PNY sticks can run at.

The other posters are correct, the only solution is to get different RAM and try those. I would also advise to use a more reputable brand, the cost differences are minimal and the warranties are better.

Yes. I own a MacBook Pro 3,1. I installed 6GB memory and have been using it like that for more than two years. Note the specifications below. You can call the tech support people at Other World Computing if you have any questions.

The RAM in my system is as follows:

• Bank 0: 2GB DDR2 SDRAM 667 MHz
• Bank 1: 4GB DDR2 SDRAM 667 MHz