A magnetic disk information storage apparatus comprises a head/disk assembly removably mounted in a housing assembly. The head/disk assembly encloses rotatably mounted disks, and accessing heads mounted for linear movement on a carriage. Fixed to the carriage and therefore part of the subassembly is a linear actuator coil. The linear actuator magnet structure which cooperates with the coil to produce motion of the carriage is located in the housing assembly. Loadings of the subassembly into the housing assembly locates the actuator coil in a magnetic flux gap of the magnet structure.