Well, I recently decided to upgrade my Macbook to 4GB of RAM. I can get by with just 2GB, but I had an excuse to spend some money before March 31. Anyway, I thought I did the right thing. I bought some Hynix RAM. I keep reading forum posts about Apple using Hynix in most of their machines (and indeed the existing RAM in my Macbook was Hynix brand). I also knew that the Penryn Macbook I have takes DDR2-667 SODIMMs. But I went and searched online and was going to buy some Hynix 2GB DDR2-667 SODIMMs from an online retailer, when I noticed that they also had “Hynix 2GB DDR2-800 SODIMMs ‘for Mac'”. Those words ‘for Mac’ are compelling when you know from past experience that laptops can be very fickle when it comes to RAM.
So I bought the Hynix DDR2-800 memory. I put it in and my poor Macbook would not boot at all. I put the old 1GB DDR2-667 SODIMMs back in and it worked again. Then I tried one of the old 1GB DDR2-667 SODIMMs and one of the new 2GB DDR2-800 modules and it booted up and worked fine. I also tried the other 2GB DDR2-800 modul with one of the old 1GB DDR2-667 modules and it also worked. In both cases the ‘About this Mac’ screen also said it had 3GB of RAM.
So I trawled google and the general view is that Penryn Macbooks cannot use two DDR2-800 SODIMMs. They can use one DDR2-667 and one DDR2-800 SODIMM, but somehow the chipset does not want to play if two DDR2-800’s are inserted. Grrrrr.
So I’ve returned the memory, and I bought some Kingston memory (the 4GB kit ; KTA-MB667K2/4G ) instead which even the Kingston site says is the right memory for my Macbook. And suffice to say the new memory works perfectly.