ONE MORE RAM USAGE UPDATE! Saves about 130 MB more RAM.
To save alot of RAM and not to get MAF's by RAM usage in late game turn on viewport option in "BUG" reduced my RAM usage from 1600 MB to 1100 MB! So larger maps will work even better.
How to do it:
1. Open "BUG" in game, (Green BUG icon in game upper left) select on first tab "Enable Viewport".
2. Set "Viewport" horizontal size to 232 and set "Viewport" vertical size to 112, thats the exact earth size without space then jumping to combat works and it saves you 300-600 MB RAM usage. (Can be lowered if more RAM is needed later)
3. Restard the game completly to enable viewport correctly.
4. Before restarting turn off in steam "Steam overlay in game" and "VR Cinema modus in game" - Right click Civ IV Beyond the Sword in steam then click properties. Saves about 100 MB more RAM. Also under "Controller" in steam Civ IV properties deactivate, steam input devices = saves 30 MB more RAM.
Lower RAM usage and no MAF by RAM for a long time. (Only needed if you run low on RAM, but you can use it at gamestart also.)
Works fine on WIN 10, Win 7 or 8 needs more RAM.
I will put this on first page here to the installation instructions.