We're still waiting from someone with enough money to blow on an experiment to clue us in. I'm sure it will happen eventually and word will make it here when it does.
I see no reason for it not to work. The MBP uses the exact same chipset and cpu as the IBM T60 series and they support the 2 x 2GB configuration.
The only reason that there might be an incompatibility is if there is some sort of problem due to the fact that Apple uses EFI instead of BIOS. However, EFI is the new standard so that's not likely.
You could call Apple support and ask them otherwise wait until someone gets to test it out.
This has been discussed a lot. We know the hardware can address it all because other systems that use the same chips can succesfully use 4 GB of RAM. But that does not guarantee that something in the MacBook's or iMac's memory management does not preclude using all 4 GB of the physical address space.
Until some tries it or Apple issues a statement that explicitly says 4 GB will or will not work, we just don't know.
By the way, it is by no means only the boot and BIOS code that have to be compatible with 4 GB. If anything, it seems to me they're less likely to have an issue. Apple's implementation of paging could conceivably impose the 2 GB limit that Apple states.
You're right kkapoor, the chipset is the same. Idk whether the EFI vs BIOS would pose a problem with the system recognizing 4GB though. It seems to me that Apple would specifically say not to do this if it could damage the system in any way. The reason I ask is because I'll have this system for around three years, and running out of memory is the last thing I want to deal with.
Now there's a trade-off I would
not make. Most of the incredible speed of the iMac and MacBook Pro come from the 667 MHz memory speed.
I have a system with 400 MHz RAM and when running some nominally CPU-intensive code on a 3 GHz Linux system (the code is single threaded, so dual processor Mac vs. HyperThreading Linux box is not probably an issue, and it's Java, so the direct speed comparison should be meaningful), the Mac beats the Linux box by—get this—~50%!
In other words, the speed difference is all about the RAM speed. The processor is often waiting for data, and that makes the RAM and the interface to it the bottleneck. At least with today's processor architectures. Some of what I've been reading about the next generation of Intel processor suggests that they're improving the efficiency with which the CPU access main memory, but still, for the foreseeable future, RAM will be the limiting factor in raw performance, as it has been for quite some time, now.
