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I ran a program called 'fwmemmap' which executes the int 15h function E820h to get the memory map created by the firmware and then passed onto the OS. I am running 64-bit Windows and have 8GB of memory installed. Below are the results -
The total of all type 1 (memory) adds up to 8142MB which is correct and is also correlated in Windows -
When I total up the size of the reserved address space it equals around 105MB which is more than is physically installed. Why does the firmware do this? Are these address used for some chipset devices (The tool doesn't collect addresses used for MMIO devices, just system memory).
My next question is how does Windows also know that the total memory installed is 8192MB? Where is it getting the 50MB 'Hardware Reserved' from out of the memory map. If the memory map shows what address space is reserved, how does the OS know which part of physical memory is reserved by the BIOS?
Any help with these questions would be greatly appreciated,