Yes, as long as there is available RAM, ARCHICAD will use as much as it needs. ARCHICAD 19 is 64-bit only so there is no 4 GB limitation to the amount of RAM it can use, like 32-bit applications have.
As a side note, I have 16 GBs of RAM and there was only one time, when I was testing the limits of ARCHICAD when I ran out of RAM. So in normal practice I never reached this limit. However, next summer when I buy a new laptop I will have 32 GBs of RAM in it so it will be enough even in 2020.
RAM for me is the single most important component of a CAD workstation.
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