Don&#x27;t forget the BSP tree, that&#x27;s what really made Doom work and be playable with huge maps on a 386 &amp; 486.  By cutting the game map into sections in front and behind the player it could very quickly figure out a small set of sectors that are visible and just render them instead of the entire world (which would be way too slow on computers of the time).  Fabien Sanglard has a great analysis of how Doom worked: <a href="http:&#x2F;&#x2F;fabiensanglard.net&#x2F;doomIphone&#x2F;doomClassicRenderer.php" rel="nofollow">http:&#x2F;&#x2F;fabiensanglard.net&#x2F;doomIphone&#x2F;doomClassicRenderer.php</a>