Today we are looking at 4GB of PC2-6400 SODIMM RAM from Crucial for use in a notebook computer. To get the full benefit from 4GB of RAM, you need to have a 64-bit OS. I was very impressed with the performance of the Crucial 4GB DDR2 PC2-5300 RAM in my Vista Ultimate machine. I wholeheartedly recommend that anyone running Vista seriously consider a RAM upgrade, it can make a huge difference in your performance.