Note you're comparing two entirely different graphics technologies. Your 2009 iMac has a dedicated or "discrete" GPU--a mobile version of a more powerful desktop GPU, but dedicated nonetheless. The Mac mini (and any Macbook less than 15") only has a GPU integrated with the processor, and uses system RAM for video memory. Integrated GPUs are a crutch for budget systems, or systems too small to handle dedicated GPU and their heat. It will handle the fancy OS animation effects, common video formats, and basic games. For what it is, the HD4000 isn't actually *that* bad, but just like you don't want to run a marathon on crutches, you don't want to try serious games or X-Plane using an integrated GPU. It can technically be done, but you won't like the results