You should run you own software under subpar conditions with advised window settings for large RAM applications. You are wrong. It's exactly why virtual memory exists. Out of Physical RAM. That's why you never see message about physical ram but out of virtual memory because that's the last fail safe of memory to use in any event while RAM is allocated to something else. For example allocate almost all usable memory to a RAMDisk and than start running programs.off disk. It's crucial to system stability and default settings ARE NOT appropriate for rendering, let alone Photoshop or something less intensive. Virtual memory is a layer of the windows memory complex, part of RAM management. If a program tries to allocate more RAM than available, it is given virtual memory, while much slower. You can see this in real time with your memory diagnostics. However if it can allocate more memory, such as a program not holding on to it's memory, it will cache things not in use from RAM to free up RAM. This is why RAM allocation is crucial for things like RAMDisks, rendering, gaming, etc. As part of paging, this is also crucial for windows processes and services, as well as inactive programs you have running.
There's a reason editing size restrictions for performance on low RAM systems is advised across Winodws, Mac and Linux.. I can play games that require 8-16 GB ram such as KSP modded which with real scale solar system and planets, because of edited virtual ram, or I will run out of RAM and get a out of virtual memory and WDM start crashing along with the game.
Additionally on default settings like installing Windows on this new machine I could not render multiple 10k pops. Fine with virtual memory expanded to 12gb. This has always been a RAM limit until I discovered this with TG. Like in the past where I could only manage one population like my forest mountain seen back from like 2015.
Does Terragen even allocate memory? That should be a feature for actual renders.