Is it possible that a Mac laptop could show 768 mb of SDRAM when you click on the apple at top left and then "About this Mac" and yet only be capable of using a smaller amount of the installed RAM. The reason I ask is that my laptop had 2 memory sticks installed. A 128 pc100 and a 256 pc100. This showed up as 384 mb in "About this Mac". I removed the 256 stick from the top slot and replaced it with a 512 mb stick of pc133 RAM. The memory shows as 768mb and according to "About this Mac" >> Memory ... all is well. The laptop just seems a lot slower. ps .. I have a 512 stick of pc133 on order so this may be a moot question.