How much you need depends on what you do (and to a degree how you want to do it), for most people about 8GB is enough, if you do a lot with photos, video, CAD or use othr memory centric programs then might want to think 16GB....As PyjamasCat said it is used as a temp storage area and is where the CPU sends instructions to do calculations, redrawing etc....if you are ever sort of jumping around the net, working with a program, have a number of windows open, etc and notice your HD LED blinking a lot, it normally means more DRAM/memory may be in order....when that led is blinking it's generally that pretty much your DRAM is full and rather than just let the data disappear, it writes it to the page file on your hard disk, then when it wants that data back, it simply reads it off the hard drive which slows you down a bit, but is faster than it having to pull all the data from the internet again, or have to load an entire data file off the HD again