What is Ironman? Just no more then one save per game?
Ironman is a concept where you can't make backups of your game in any way (In theory). Basically it means that you can only save to exit the game, and only load to start the game.
No more "Just in case" savegames every few years, or before a decision. Everything you do is set in stone and can't be avoided by loading an older save.
Ironman mode is also the only way to gain achievements.