# How much number crunching is necessary in some simulations?

• I
I've seen simulations like these, simulations that were done in *very* gory detail, and simulations that apparently required a large number of CPU cycles and a large amount of memory space.
• Cosmological structure formation and galaxy formation
• Collisions of galaxies
• Formation of planetary systems and collisions of planets
• Inspiral of black holes or neutron stars
Does anyone have any more details on any of that? Like what computers that they used and how long that they needed for a run.