See
here for a table of Agnus versions. If I'm right the standard Agnus only sits in OCS machines (max 512k chip mem), ECS machines have Fat Agnus supporting max. 1mb of chip mem, or Fatter (Obese?) Agnus supporting 2mb of chip mem.
I could be mistaken though. In AGA machines the role of Agnus has been taken over by Alice.
