Since I receive a lot of issues with "How many Web Applications can be running in the Same Application Pool ?" .. Here is your answer ..
For who has no previous experience on this, Here are some tips for designing your SharePoint implementation:
- Do not run more than 10 Web applications per application pool until you have some performance monitoring experience behind you and you can point to your own numbers, which tell you that your application pools can handle more virtual servers.
- Do not plan to run more than 20 Web applications on a single physical server without adding a second Web server (or more) in your farm. The reason for this is because if you're running 20 virtual servers, you've got a growing, busy farm and chances are good that you should scale out before you scale up.
- Always purchase servers with 4 GB of RAM to give yourself maximum flexibility in memory allocation for your application pools.
- Make each application pool a Web garden with two or three worker processes associated with it. When stsadm.exe runs, it locks one of the threads for its own use. Having other threads available to service calls during backup/restore operations or other scripted operations using stsadm is necessary in most environments. In addition, if a thread becomes very busy, the other threads can pick up the slack.
Source: MS SharePoint Server 2007 Administration Companion Book