IRS, Flight Control Computers and such components in simulation are often software emulations. There are very detailed specs from the manufacturer available in the data packages, which allow you to design such models (think Matlab/Simulink compiled to code).
The simulators I work with (737NG) have the EGPWS, the FMC and the DU software either re-hosted or real aircraft boxes. All the rest is simulated. Well, other components like yokes, pedestal and other panels also can be aircraft parts (refurbished). But as far as we are speaking about avionics....
Last edited by Flutter speed; 7th December 2012 at 06:18.