The W3WP.exe is the IIS worker process, that handles requests, maintain sessions, viewstate, and the cache. Its been around Since IIS 6 on Windows Server 2003, and is still found as part of IIS 7.5 with Server 2008 R2. On a properly configured, and programmed website the W3WP.exe can usually stay under 100 Megs. If you are running a 64bit OS it could be a little larger. The actual size of the W3WP.exe will be determined by how much traffic your website gets, and how many pages it serves. The 100 Meg figure is just an estimate from my own experiences. Application Pools with multiple websites can easily go over this figure, so don't use it some magic number. But if you are running a website that has relatively low traffic ( under 20K impressions daily ), and your W3WP.exe is taking up 100+ MB of Memory, then you might want to make some changes