I have a laptop with 4 GB RAM and Windows 7 Enterprise 64 bit edition installed. With my regular office work I end up consuming around 3.9 GB of system memory (because I run a virtual machine), and at this point I used to get a very bad performance because the hard disk used be continuously accessed. Couple of weeks ago I got frustrated and ordered for 8 GB RAM for my laptop, think that that was the only solution. And guess what, the amount quoted by the dealer for the RAM was 5 times the market rate, so my request was rejected (quite obvious).
Then I started tweaking my OS settings so as to reduce the memory footprint. I started with disabling aero, disabling unwanted services, uninstalling programs etc.. But this did not reduce the memory consumption or improve the performance with the RAM consumption was around 3.9 GB. So as an experiment I disabled Superfetch service, and voila the performance at 3.9 GB RAM consumption became much better. I guess Superfetch is designed to keep the RAM filled with data which it thinks might be used by the user in the coming future, and as the available RAM was very less, it was not doing a very good job and resulted in lot of prefetching and hence high disk activity.
Disabling Superfetch reduced the disk activity drastically