The door on the 550c is removed, and some trim on the 520c is removed, showing the external interfaces. Ports from left to right are: Power in, printer/modem, sound in, sound out, ADB, AAUI, monitor out, SCSI (HDI-30 connector), modem port, and Kensington key-lock. Note the 550c hinge cover is darker. Note the labels on the door needed to identify the internal modem (FCC info on the "PowerPort" label, Canadian on other two). The 100–240 V power supply is on top.