Didn't Airbus employ 5 different companies to write the FBW software for the A320 family? I believe on the B777 all the flight control software is written by the same company. I know which I think is the more sensible approach.
A4
Do you? It is referred to as 'dissimilar redundancy' so one error will not manifest itself in other programs. Also different chips.
IF you were to study the FBW control system, you would see that different chips and different software is controlling different surfaces so a lot can go wrong before you lose (or 'loose' as is often the word used on the net
) control. Not a bad idea.