Address Space and Virtual Memory

Remember? : We covered it in the context of processes and threads.

• It constitutes all the addresses a program can touch. All the state that a program can affect or be affected by
• There are generally two views of memory :
  One view from the CPU : What the program sees : Virtual Memory
  View from the memory : What exists in practise : Physical Memory
• The memory management unit (MMU) translates the CPU (program) addresses into real (physical) addresses
• The translation via MMU helps to achieve protection, as no two programs can access the same physical memory
• The translation via MMU can take place by a number of different methods, which we shall now discuss
• Similar to one person giving orders, another person interpreting these orders and performing activity (also somewhat like macros - a simple name can mean many activities combined together).
• Modification of the translation table can only be done by kernel (in supervisor or previledged mode)
• So, user program can only affect its own address space, kernel can affect all address spaces