If you study the specifications of the recently released Core 2 Duo-based Apple MacBook Pro, you may be puzzled by the quoted RAM limit of 3GB. The notebook has a pair of DIMM slots that can accommodate 2GB modules, while the Intel 945PM chipset -- which this MacBook Pro model uses -- can handle 4GB of RAM. So why doesn't Apple specify a 4GB RAM capacity?
The reason, it seems, is that Apple is trying to save its customers from installing extra RAM that can't actually be addressed by applications and user data: according to Softpedia (quoting macfixit.com), a number of system functions, including PCI Express RAM, occupy the address space between 3GB and 4GB, making it unavailable to users even if RAM is physically present.
This, of course, applies to 945PM-based Windows systems too, but most other vendors' spec sheets still quote a 4GB RAM capacity.
We're not talking peanuts here, either: to upgrade the 2.33GHz MacBook Pro from its standard 2GB to 3GB will cost you a cool £380 (ex. VAT).