I go onto alot of customer sites and am constantly evaluating the performance and configuration and advising best practise on Domain Controllers. Often the Support team has configured the /3gb switch in their Boot.ini files.....many of them do not know why ? or say "The Exchange Team insisted upon it ". Well if you want the low down and "demystifying" of the /3gb switch then check out this blog entry from the ASKPERF blog. This explains perfectly the "why" and the "how" of the /3gb switch and what effect it has on your 32bit memory environment.