Kappy wrote:
PC2-4200 RAM is not PC2-5300 RAM. The former is DDR2 533 MHz and the latter is DDR2 667 MHz. You cannot use the former if your computer requires the latter. Your model requires DDR2 667 MHz PC2-5300 RAM, not PC2-4200.
Actually it should work but with what should be an obvious performance penalty. I've tried it (used PC2-4200) myself on my late 2007 model when I was bored and had access to some PC2-4200 modules from another computer that was upgraded. I've read the Intel chipset datasheets, and they've always had backwards compatibility in mind. The MacBook4,1 designation is for the last of the Intel chipsets. I'd also take a wild guess that the NVIDIA chipset versions might work with PC2-4200, although it's been reported that they work with PC2-6400.
If PC2-5300 is mixed with PC2-4200, it should read as DDR2 533 in system profiler. The default when speeds are mixed is to run both at the same speed. I tried all sorts of combinations including 2 GB (PC2-5300) + 512 MB (PC2-4200), 2x512MB PC2-4200, 512 MB (PC2-4200) + 512 MB (PC2-5300).
Apple doesn't exactly tout this as a feature, but in my experience it will work. It's not an ideal solution and frankly I wouldn't go out of my way to get PC2-4200. However - I've tried it myself out of curiosity and found that it did work - at least in my machine.
