is the RAM that is unmapped being used?

Hi,
generally, in a 32 bit system. if the RAM is of 4GB. only 3.28GB is mapped into virtual address space and the rest of the address space is used for register mapping.
I wanted to know weather the RAM that is not mapped into virtual space is being used or left unused.
Please reply.

Code:

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grep "MemTotal" /proc/meminfo

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Hi, Thanks for replying.

meminfo reads the information from DDR Controller and prints the information.
But, My question is weather the virtual/logical mapping exists for entire RAM

I don't think this is really a linux question, per se. You may want to check wikipedia.