is there a way of calculating the amount of ram without using the bios interupts??

You can scan it until you either find it wraps around or you can't set the value. But be careful of memory mapped I/O, you might cause something to go astray.

Another way is to read the config directly from the chipset, maybe you can download a spec sheet from the MB manufacturer.

the paging can be used
set a page to the current 4k to test
if the memory is available, then you can read form the offset 0 of the page
increment the Page base
you can then test for all the 4G
and then set a Page Table with present flag updated


but, the ram is not always the one for the µP, the specific ram for graphics will be included, the same for several extensions.

so, the method that revolution told to you seems to be good, but dependant on hardware...
and asm coders want to do all by themslve

Yes, read SPD ( Serial Presence Detect) from eeprom of your RAM module trough SMBus

Use the BIOS and avoid problems with reserved memory areas...

probing memory manually is a bad idea, unless you're writing a BIOS memory detection routine and know wtf you're doing, including (but not limited to) the exact chipset you're targeting.