Tech, ExplainedNetworking, infrastructure and security
Concept

Server racks

Tall frames, dozens of servers each.

HOW IT WORKSEach server is a flatbox of 1U or 2U heightServers slide into theslots of a 42U rackPower strips at theback feed each serverCables go to a switchat the top of the rackCool air enters at thefront and hot airleaves at the backA standard frame lets any maker's equipment be added, replaced, powered and cooled in the same way.HOW IT WORKSEach serveris a flatbox of 1Uor 2U heightServers slideinto theslots of a42U rackPower stripsat theback feedeach serverCables go toa switch atthe top ofthe rackCool airenters at thefront and hotair leaves atthe backA standard frame lets any maker's equipment be added, replaced, powered and cooled in the same way.HOW IT WORKSEach server is a flatbox of 1U or 2U height↓Servers slide into theslots of a 42U rack↓Power strips at the back feed each server↓Cables go to a switchat the top of the rack↓Cool air enters at the front and hot airleaves at the backA standard frame lets any maker's equipment be added,replaced, powered and cooled in the same way.
Servers slide into numbered slots in a standard metal frame, which supplies power, a network switch and a flow of cool air.
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Server racks are tall metal frames that hold dozens of servers each. A standard rack is about two metres high and 60 cm wide, with slots for equipment stacked from bottom to top. Data centres are made of long rows of racks. Each server is a flat box that slides into one slot, so a rack can hold 20 to 40 servers, or more.

Here is how a rack works in general. Equipment sizes are measured in a unit called "U", which is 4.4 cm of height. A server is 1U or 2U high, so a 42U rack holds up to 42 small servers. Power comes through strips at the back that feed each server, and cables go to a switch at the top of the rack, which joins the servers to the rest of the data centre. Cool air is blown in at the front, passes over the hot parts and leaves at the back. Putting equipment in racks makes it easy to add, replace and cool, and keeps the cables neat.

Rack equipment is 19 inches (48.3 cm) wide across its front panel, which is the standard width. The opening between the rails is about 45 cm. A full rack can weigh several hundred kilograms, so the floor must be built to carry it. The power for a rack is limited. An ordinary rack takes about 10 kilowatts. An AI rack takes 40 kilowatts or more, and the newest take over 100 kilowatts. The cooling must match the power. Racks face each other in rows so that cool air comes in at the front of one row and hot air leaves at the back into a shared hot aisle. This keeps hot air from being drawn back into the servers.

Take, for example, a company that runs its own computers in a rented room. It fits twelve servers and a switch in one rack and pays for the space and power; see colocation. Consider a cloud company, whose rack of graphics processors for AI may draw 40 kilowatts or more and needs special cooling; see AI clusters. Imagine a telecom exchange, which keeps its switches and storage in racks as well.

Details appear in racks inside the data centre, data centre power, servers, storage systems and switching. The wider picture is in inside a data centre and bandwidth and latency.

How is it different from a cabinet or a shelf? A rack follows a standard width and height, so equipment from any maker fits, and all of it can be powered and cooled in the same way.

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