How is the Virtual address space greater than Physical address space ?
suppose a Virtual 0x7000 maps to physical address 0x8000, can another virtual address lets say
0x7500 map to the same physical location as 0x8000, if not then how can there be more virtual
address and limited physical memory since mapping has to convert to physical address?
Please help me understand this concept.
http://en.wikipedia.org/wiki/Virtual_memory.
Virtual Memory uses both physical ram and hard disk space to represent more memory than may physically exist, and provides an interface whereby each program can request memory resources without having to be concerned with the other programs existent on the machine and which memory addresses they may request.
The whole virtual address space does not have to be mapped to physical memory at the same time. That's what makes it "virtual". The contents of that virtual memory which is allocated but not currently mapped to physical memory reside on some form of external storage, typically disk.
It is the memory management system's job to move virtual memory pages into and out of physical memory as needed, and the requirement to do so is why virtual-memory computers can slow down overall when enough memory is allocated that it no longer all fits in physical memory at the same time.
