Question

For each process a separate memory is allocated. In .net the process can contain multiple app domains. How the memory is allocated for each app domain? Do they share the common memory of the process?

Answer 1

No they are not allowed to access the same memory and share objects in this memory space, objects should be marshalled when you pass them from one app domain to another one:

Application Domains

Code running in one application cannot directly access code or
resources from another application. The common language runtime
enforces this isolation by preventing direct calls between objects in
different application domains. Objects that pass between domains are
either copied or accessed by proxy. If the object is copied, the call
to the object is local. That is, both the caller and the object being
referenced are in the same application domain. If the object is
accessed through a proxy, the call to the object is remote. In this
case, the caller and the object being referenced are in different
application domains. Cross-domain calls use the same remote call
infrastructure as calls between two processes or between two machines.
As such, the metadata for the object being referenced must be
available to both application domains to allow the method call to be
JIT-compiled properly. If the calling domain does not have access to
the metadata for the object being called, the compilation might fail
with an exception of type System.IO.FileNotFound