An S7-400 system basically comprises a rack, power supply, and central processing unit. It can be installed and expanded in a modular way. All modules can be positioned freely next to the power supply plugged in on the left. The S7-400 has a rugged design without a fan. Signal modules can be hotswapped.A multi-faceted module range can be used for central expansions as well as for simple configuration of distributed topologies with ET 200.In a centralized expansion, additional mounting racks are connecteddirect to the central controller.In addition to the standard mounting racks, aluminum mounting racks with 9 and 18 slots are also available. These aluminum racks are highly resistant to unfavorable environmental conditions, and they are more rigid and around 25% lighter.