Codici di calcolo are the actual codes used to perform the computer simulation. Normally in English they are simply called "codes", while Italians like to be more specific...You could also use "numerical codes", but I think it isn't that common. Typically the main code consists of several shorter codes linked together, that's why one talks of "l'insieme dei codici di calcolo". And the "dati utilizzati" are the data required to start the simulation, technically called "initial conditions".

I used to work on computer simulations in my previous "life" before joining the translation world...

Buon lavoro,
Costanza