FMGC (Flight Management Guidance Computer) for Bus, and FMC (Flight Management Computer) for Boeing.
They both achieve roughly the same thing as implied by their names.
I personally find the FMC somewhat more user friendly, but that is probably because I've had far more exposure to that machine rather than only 2 years on the FMGC.
Both have advantages and disadvantages when compared to the other. Bit like the ongoing PC versus MAC argument I would imagine.
Anyway, back to my mince pies before I get another ticking off!
Happy Christmas
Regards
Exeng