x86 memory detection

[Arun S]

Hi,
 How does the kernel detects the amount of available System RAM in the
system under x86 architecture?.

Under 2.6.x kernels,


1. Does it use BIOS interrupt 15 for determining the RAM

 OR

2. Does the boot loader fills the e820_map as explained
inDocumentation/x86/boot.txt &   Documentation/x86/zero-page.txt  and the
kernel uses in information

OR

3. Is there any other mechanism (if so, in which file under kernel tree I
can find this detection code)



Thanks,
Arun
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