Could you explain more about what your experiment was actually doing and share the results?
Cross-AppDomain calls within a single process to share a thread, so the overheads will be lower. But there are still overheads - it has to go through a fair amount of infrastructure in .NET to switch AppDomains even though it avoids a thread switch. (It ends up going through the Remoting architecture in fact, and does a lot of the same work that it would have done for a cross process call.) -- Ian Griffiths DevelopMentor -----Original Message----- From: wycklk [mailto:[EMAIL PROTECTED] According to Microsoft, threads can execute across AppDomains without the overhead associated with inter-process communication and process context switch (vs thread context switch). I did an experiment to verify the above. However, I found there is no obvious performance gain when I use 2 AppDomains within one process vs 2 separate process. My focus here is on performance and scalability Anybody can share his experience ?