An image formation apparatus contains a first and second unit. The first unit, which is a self-contained first module, contains a photo-sensitive body and structure for removing residue toner from the photo sensitive body. The second unit, which is a self-contained developer module, provides toner to the first unit and receives the residue toner from the first unit. The residue toner in the second unit is received in a self contained container and does not mix with fresh toner. The modules are detachably mounted in the apparatus. The second module cannot be mounted in the apparatus until the first module is mounted. The two units have different lives of interchange.