Just out of curiosity, are all of the Flight Control Computers located in the same physical place on FBW aircraft, such as the A320 ? In my job (IT), it's best practice to have redundancy of not just data, but of the hardware - including having the failover system in a different location.
The A320 series FAC, FMGC units, the core of the FBW system, are located on the same equipment rack within inches of one another in the avionics bay, however they are contained within metal boxes and are powered by separate busses for redundancy.
One some other aircraft, this arrangement is further enhanced by physically locating any dual/triple redundancy (flight critical) units about a meter away from one another.
Design differences aside, the level of power (available current and voltage) input to computer IRU's is low enough to prevent a catastrophic failure of one box from affecting its neighbouring unit, even if they are installed right next to one another.