Witch ecu's are interchangeble?

[Sjoerd320i]

Right, My ecu is half dead, the car is running on 5 cilinders.
I tested a mates ecu and everything is fine again.

I now have a 400 ecu and he has a 403 and that worked fine.
If I check BMWfans.info I see that the another ecu (402) is used in a 520 as well as a 525 m50.

Will the programming be different between those two or are they self learning so I can fit one from a 520?

[hongkongfuey]

i was looking up my one which is a403 which looking up is e34 m50/b25. i had this in my e36 325 non vanos which ran perfectly
i know on the e30 you can use the 320 ecu but it needs to be chipped