Remember that it takes more than just the filesize in Ram to perform calculations. For things like levels, it's not going to make a huge difference, but the multiple undo's alone have to be stored somewhere, and that somewhere is memory. So every time you perform an operation, the pervious states are saved in the memory for multiple instantaneous undos/redos. I shoot on 35mm slides and scan them in at about 25MP. Sometimes I shoot medium format film and scan that in to 90MP. It the medium format scans that give me trouble. They are 500 megs each and doing anything more than levels takes a WHILE. Especially the median filter, because it averages a certain number of pixels in each direction, and that's a LOT of pixels to average in a lot of different directions, in excess of 128 billion calculations. I was also recently making a large format digital print in which I decided to collage some screen shots I took over a photo of oil drills in the desert. I blew up the oil rig photo to 12,600x21,600 pixels (6x3.5 feet at 300DPI), and then overlayed the screen shots and started working. Layers are especially slow, because it treats each layer as a separate full sized image and must store each layer's pervious state in the history. With layers, the final image size was over 5 gigs, which I wasn't about to save to my ipod LOL. FLattened it and saved as a tiff it was about 800 megs. Cool print too :) Onb that last oe though even the "paltry" 8 gigs of RAM were not helping all that much :)