MacBook Pro and 3GB RAM Limit

I was surprised to see that the newest MacBook Pro memory can only be upgraded to 3GB. Since the laptop has two memory slots one would think with 2GB memory chips you can easily (for $625 a piece) upgrade to 4GB.

Jason D. O'Grady and MacFixIt explain that it is not that simple, Intel's 945PM chipset has limitations:

The MacBook Pro Core 2 Duo presumably uses Intel's 945PM chipset, which can physically handle 4 GB of DDR2 RAM. However, a number of items that must be stored in physical RAM space, and when RAM reaches 4 GB, there is some overlap. In other words, in a 3 GB RAM configuration, there is no overlap with the memory ranges required for certain system functions. Between 3 GB and 4 GB, however, system memory attempts to occupy space that is already assigned to these functions. For instance, the PCI Express RAM allocation occurs at somewhere around 3.5 GB of RAM and requires 256 MB of RAM. Thus, the virtual space between 3.5 GB of RAM and 3.75 GB of RAM is occupied by PCI Express data. So in a system with 3 GB of RAM, nothing is being wasted because the memory space required by PCI Express is still between 3.5 and 3.75 GB, and the installed system RAM does not violate this space.

The net result is that at least 3 GB of RAM should be fully accessible, while when 4 GB of RAM installed, ~700 MB of of the RAM is overlapping critical system functions, making it non-addressable by the system.

Oh, well... I guess I just have to limit myself again; as always ;)

Comments

[bravomail]

To me sounds like a bullshit. I know for fact that WinXP x32 has 3GB limitation. And more over WinXP x64 does not have such limitattion. But Core Duo is 32-bit, so may be there is some connection, but...