The "HD" version is an updated release designed to make the original DOS/Windows 95 game playable on modern hardware:
Regularly features the HD version in "Strategy" or "RTS" bundles for a few dollars. Earth 2140 HD Free Game Download
You may find sites offering the game for free, but proceed with caution: The "HD" version is an updated release designed
Usually bundles the original game with the Mission Pack 1 and Mission Pack 2 (Final Conflict) . Earth 2140 HD Free Game Download
Play at resolutions like 1920x1080 without extreme pixelation.
Check sites like ModDB for community patches that improve the legal version of the game rather than downloading cracked files.
Fixed "too fast" gameplay issues where the engine ran at the speed of your modern processor. ⚠️ A Note on "Free" Downloads