why each process is loaded to the main memory for execution?

Answer 1

each process is being fetched up to the processor, and the processor itself uses the memory to run the process.. that's just it. a processor cannot work without the memory...

Answer 2

To understand the memory model of the 32-bit JVM for AIX, you first need to understand the address space of 32-bit processes on AIX. Various address space models on AIX were discussed at great length in the Developing and porting C and C++ applications on AIX Redbook, form number SG245674, and in the AIX product documentation the General Programming Concepts: Writing and Debugging Programs, the chapter on Large Program Support. Though we'll describe the address space models that are pertinent to the discussion of Java memory model, it is highly recommended you read both of these documents, especially if you use JNI in your Java applications