ZF gearbox query

Got some questions regarding the ZF gearboxes fitted to the e90 and e60 range, all the 6cylinder petrol motors come with the 6hp19 gearbox, are these gearboxes internally identical between them and a different final drive ratio or is there differences in the gear ratios etc...

Which vehicles did the 6hp21 come fitted on? I have checked realoem and mine is a 6hp19, looked at a buddy's 2009 and his is also a 6hp19...

Ironically the 525 and 530i also came with a 6hp19 box, are all these gearboxes interchangable?

Thanks!