Current MacBook Pro models, iMac and new MacBooks allow you to install up to 3GB of RAM with 1GB and 2GB modules. However, as practice shows Such a configuration not only does not lead to an increase in the performance of the entire system, but even loses the configuration speed with 2GB of RAM when installing two paired 1GB modules.
Other World Computing, which compared the speed of a new MacBook Core 2 Duo in a configuration with 2GB and 3GB, also prove this.