title: What are the differences between virtual memory and physical memory?
body: <p>I am often confused with the concept of virtualization in operating systems. Considering RAM as the physical memory, why do we need the virtual memory for executing a process?</p>
  
  <p>Where does this virtual memory stand when the process (program) from the external hard drive is brought to the main memory (physical memory) for the execution.</p>
  
  <p>Who takes care of the virtual memory and what is the size of the virtual memory?</p>
  
  <p>Suppose if the size of the RAM is 4GB (i.e. 2^32-1 address spaces) what is the size of the virtual memory?</p>