In the Top of Rack design servers connect to one or two Ethernet switches installed inside the rack. The term “top of rack” has been coined for this design however the actual physical location of the switch does not necessarily need to be at the top of the rack.
Each rack is connected to the data centre with fibre. Therefore, there is no need for a bulky and expensive infrastructure of copper cabling running between racks and throughout the data centre. Large amounts of copper cabling places an additional burden on data centre facilities as bulky copper cable can be difficult to route, can obstruct airflow, and generally requires more racks and infrastructure dedicated to just patching and cable management. Long runs of twisted pair copper cabling can also place limitations on server access speeds and network technology. The Top of Rack data centre design avoids these issues as there is no need to for a large copper cabling infrastructure. This is often the key factor why a Top of Rack design is selected over End of Row.

In the End of Row server cabinets (or racks) are typically lined up side by side in a row. The term “End of Row” was coined to describe a rack or cabinet placed at either end of the “server row” for the purpose of providing network connectivity to the servers within that row. Each server cabinet in this design has a bundle of twisted pair copper cabling containing as many as 48 (or more) individual cables routed to the end of row. The end of row network racks may not necessarily be located at the end of each actual row. There may be designs where a handful of network racks are placed in a small row of their own collectively providing end of row copper connectivity to more than one row of servers. For redundancy there might be two bundles of copper to each rack, each running to opposite end of row network racks.