from the rack. Slides or rails for computers and other data processing equipment such as disk arrays or routers often need to be purchased directly from the equipment manufacturer, as there is no standardization on such equipment's thickness (measurement from the side of the rack to the equipment) or means for mounting to the rail. A rails kit may include a cable management arm (or CMA), which folds the cables attached to the server and allows them to expand neatly when the server is slid out, without being disconnected. Computer mounting Computer servers designed for rack-mounting can include a number of extra features to make the server easy to use in the rack: The sliding rails can lock in various extended positions to prevent the equipment from moving when extended out from the rack for service. The server itself might have locking pins on the sides that just drop into slots on the extended rail assembly, in a manner similar to a removable kitchen drawer. This permits very easy server installation and removal since there is no need for the server to be held in midair while someone fastens each rail to the sides of the server with screws. Some manufacturers of rack-mount hardware include a folding cable tray behind the server, so that the cables are held into a neat and tidy folded channel when inside the rack, but can unfold out into a long strip when pulled out of the rack, allowing the server to continue to be plugged in and operating normally even while fully extended and hanging in mid-air in front of the rack. This piece of equipment thus simplifies maintenance, but at the cost of providing a restriction to airflow. Rack-optimized servers might duplicate indicator lights on the front and rear of the rack to help identify a machine needing attention, or provide separate "identify" LED indicators on both sides of the server (which can be turned on in software or by pushing an associated button). Since some configurations permit over fifty 1U servers in a single rack, this provides a simple method to determine exactly which machine is having a problem when at the rear of the rack. A handle may be provided at the rear of the server rails, to help pull or push the server without having to pull on the cables. When there is a large number of computers in a