To do MHD as efficiently as possible, the UM group took the radical step of writing a code from scratch for the Grand Challenge effort. With such huge differences in scales, a uniform grid with cells tiny enough to capture details in planets and smaller bodies is impossible on current supercomputers. An oversight module of the program acts as the driver, marking cells for division and telling them when to stop dividing according to changes in physical criteria. There is a switch in our code to do such things as the outer heliosphere, comets or the Earth. Turning on the comet switch, the group simulated the interaction of Comet Hyakutake and the solar wind.
All blocks contain the same number of cells, regardless of whether cells are big or small.
You take one processor and time it using different block sizes. This efficient approach speeds the code up in several ways. Computing multiple cells per block requires less communication among processors. You get one block fast, all the blocks are fast. A solver is a way of writing the MHD equations, including converting them into algebraic form so supercomputers can solve them.