Virtual Memory or Physical Memory

Question

Suppose we write a program in C and print the address of one of the variables declared in the program, is the address that gets printed on the screen the virtual address or the

Answer 1

In most typical cases (Windows, Linux, etc.) it'll be a virtual address.

In the typical cases like Linux and Windows, both virtual addresses and physical addresses are normally 32 bits, so having numbers in the same range becomes inevitable. It is possible to allocate more than 4 gigabytes of memory, and when/if you do so, you end up with addresses larger than 32 bits--but unless you take special steps to do that, a 32-bit address is what you'll get by default.

When you do use more than 4 GB of memory under a 32-bit OS, you're normally doing so via some special API, such as Windows' Address Windowing Extensions. Using these, you get access to more than 4 GB of RAM, but it's not what's going to happen by default with code that's even close to portable.

Some (versions of some) operating systems also use Intel's Physical Address Extensions (PAE) to give the system as a whole access to more than 4 GB of RAM, but even when these are in use, any single process running on the system is still limited to addressing 4 GB (i.e., with PAE, you can have a limit of 4 GB per process, whereas older systems had a limit of 4 GB total, divided as needed between the processes).

Answer 2

The address is going to be a virtual address in virtual memory, because the application has no knowledge of physical memory. That is hidden by the kernel and the MMU.

I am not sure what you mean by the same "bit range". If you have a 32-bit address space it will range across the entire 32-bit space regardless of what amount of physical memory you have. Likewise for 64-bit.

Answer 3

It will be a 32 bit virtual address in most cases.

If your OS supports does paging then it would be the virtual address. It could have been mapped to the same physical address using paging. Linux and Windows do paging.

Another thing that matters is the architecture. On Intel x86 32bit system it will be 32 bit address. The first 10 bits of the address will be used to get page table. The second 10 bits will be used to get page from the selected page table. And the last 12 bits will give you the actual physical address from that page.

I hope it answers your question.