a 19 inch rack

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A rack is a framework for storing things. It may hold pallets in a warehouse, an oven in a kitchen or a luggage box on the roof of a car. The type of rack found in a data center is a 19 inch equipment rack.

A data center rack may be six feet tall and full of computers and other communications devices such as patch panels. A studio rack may be two feet tall and full of audio equipment.

what it is

Soon after equipment was invented in One Million Years B.C. someone invented an equipment rack to put it in.

In computerland an equipment rack is a big sturdy cabinet that can take the weight of heavy computers. A cabinet full of computers carrying hundreds of kilos so it is best not to save money by using an Ikea wardrobe.

A full size rack is a big cabinet that is 19 inches wide on the inside, a couple of feet deep and about six feet tall. A rack has no bottom shelf so cables can be dropped straight out the bottom and run under the floor. It has a door at the front so you can get at the computer power switches and a door at the back so you can get at the computer sockets. A rack has lots of screwholes for shelves to be attached and plenty of space for cables to be tied into. These holes are in a rack rail that runs vertically in the front of the cabinet. Computers are fixed in a rack by bolting them to this rail.

a 19 inch rack
short rack patch panel mounting bracket on the patch panel

The rail holes have an odd spacing: ther are sets of three holes that repeat every 1.75 inches. This set of holes is called a U (Unit). A full size rack is about 40U high. The height of a computer that is built to go into a rack is described in Us. A computer that is 19" wide, 19" deep and 1U high is often called a pizza box because, well, it looks like a pizza box.

A rack is usually found wired into a data center. A pair of electricity cables comes out of the raised floor into two PDUs (Power Distribution Units) running up each side of the rack. A bunch of network cables also comes out the floor into a couple of patch panels (plates containing rows of network sockets) bolted to the rack rails.

Different manufacturers make their cabinets slightly different. A manufacturer may do something annoying like make its cabinets slightly too small to carry a competitor's computers or print its name in big letters on every face of the cabinets.

Racks are very expensive because they contain a fair amount of components.

  • cabinet
  • rails
  • metal rear door with air vents
  • metal front door with more air vents
  • side panels with no vents
  • PDUs
  • plinth
  • cable trays
  • velcro cable straps
  • cable ties
  • earthing kit
  • box cage nuts, screws and washers

The price list below shows a shopping list of parts for four racks. Three are for holding server computers and one is for network computers.

Description Qty Unit cost Total Cost
40U Equipment cabinets 4 £1000 £4000
Server cabinet 1 - Patch 1 1 £25 £25
Server cabinet 1 - Patch 2 1 £25 £25
Server cabinet 2 - Patch 1 1 £25 £25
Server cabinet 2 - Patch 2 1 £25 £25
Server cabinet 3 - Patch 1 1 £25 £25
Server cabinet 3 - Patch 2 1 £25 £25
Comms cabinet 1 - Patch 1 5 £25 £125
Comms cabinet 1 - Patch 2 5 £25 £125
32A power supply circuits (SWA cable, 32A commando plug & socket, circuit breaker) 8 £200 £1600
Total cost     £6000

what it isn't

where it is