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What is a rack and what does it do?

Rack Essentials

Racks organize IT equipment into standardized assemblies that make efficient use of space and other resources. At the most

basic level, a rack consists of two or four vertical mounting rails and the supporting framework required to keep the rails in

place. The rails and framework are typically made of steel or aluminum to support hundreds or even thousands of pounds of

equipment. The rails have square or round holes that allow you to mount rack equipment to them with screws. (In the case of

the square mounting holes, the screws connect to removable cage nuts placed in the required locations.) Some equipment

includes horizontal rails or shelves that you mount in the rack to provide extra support.

Rack Standards

The width of the rails, the horizontal and vertical spacing of the mounting holes, the size of the equipment cabinets and other

measurements are standardized. This ensures that standard rack equipment will always be compatible with standard racks.

Most IT equipment is nominally 19 inches wide (including mounting hardware) and follows a standard set by the Electronics

Industry Alliance (EIA) and now maintained by the Electronic Components Industry Association (ECIA). The current 19-inch

rack standard is called EIA-310-E, which is essentially equivalent to IEC-60297-3-100 or DIN 41494 in other regions. (There’s

also a standard for 23-inch wide telecom equipment. The vast majority of IT applications use 19-inch racks and equipment.)

Rack Units

Although 19-inch racks are always the same nominal width, the height and depth vary. The depth of the rack rails is usually

adjustable to some degree. The height of the rack is divided into standardized segments called rack units. Each rack unit

is 1.75 inches high, and the height of a rack or an equipment cabinet is expressed as the number of rack units followed by

the letter “U”. For example, a 42U rack contains 42 rack units. That does not mean the rack is exactly 42 x 1.75 inches high

because racks usually include at least a little extra space at the top and bottom that isn’t usable rack space. It does mean that

the rack will accommodate any combination of standard rack equipment up to 42U—whether it’s 42 x 1U switches, 14 x 3U

servers or 21 x 1U switches with 7 x 3U servers. Remember that the rack also has to be deep enough for the equipment and

rated to support the combined weight of all the equipment. 

World Class, High Quality and Economical

When you’re designing a data center, server room or network closet,
deciding which racks to deploy and how to configure them should be
at the top of your list. Just like building a house, the surface details may steal the spotlight, but it’s the quality of the underlying foundation that makes the difference between success and frustration.

Racks organize IT equipment, such as servers and network switches,
into standardized assemblies that make efficient use of space and other resources. Depending on the options you choose, they can also improve power protection, cooling, cable management, device management, physical security, mobility, ease of installation and protection from harsh environmental conditions.

Choosing the right racks and configuring them to match your needs will
ensure that your IT equipment operates reliably and efficiently, saving
your organization from costly downtime and other needless expenses. 


Server rack cabinets have become a staple in the technology world. Whether it be in data centers, classrooms or offices, they’re not hard to find. And as anyone who has worked with them knows, not all server racks are created equal. There is great variation in both the servers themselves as well as the racks that hold them. Here are just 10 different types of server racks and cabinets commonly used.

Post Server Racks
The most basic server rack is an open frame 4-post rack. These are easily assembled, and their simple 19” width frame is perfect for rackmounting equipment when you don’t have to worry about anyone poking around where they’re not supposed to. The 4-post rack provides easy access to your cabling and equipment, as well as unrestricted airflow for ventilation.

Post Relay Racks
The term relay rack has been around for over a hundred years, first used in the early 20th century for telecommunication and railroad signaling. With their small footprint, 2-post Relay (or Telco) racks are excellent for those tight spaces in your data center. This rack allows center or flush mount configuration for your equipment, and like the 4-post rack, offers easy access to equipment and maximum ventilation. Specialized kits are available to turn these simple 2-post racks into 4 point mounting.

Portable Server Racks & Cabinets
For small applications, portable server racks and cabinets are a great way to go. Need to travel? No problem! Take it along for the ride! Strong and lightweight, these mini server racks and cabinets are made to fit under desks, or on top of your counters or work station when you don’t have the space for - or just don’t need - a full size rack.

Colocation Server Cabinets
In a growing trend, some data centers, known as colocation centers, offer equipment, space and bandwidth that can be rented. When you’re sharing a server cabinet with a neighbor, you want to know that your data is completely safe. The colocation - or “colo” - server cabinet is extremely helpful in that area. Colo server cabinets provide secure, self-contained compartments for multiple tenants to share a single cabinet, so you don’t have to worry about tampering - accidental or intentional.

Air Conditioned Server Cabinets
More companies are turning off air conditioning on nights and weekends, leaving your electronic equipment vulnerable to over-heating. If you are watching the temperature gauge in your server cabinet climb to unhealthy levels, an air conditioned server cabinet may be for you. These cabinets keep sensitive electronics cool and safe in any environment using internal or external air conditioners.

Quiet & Soundproof Server Cabinets
Servers aren’t just hot, they’re loud as well. And working in a room full of noisy equipment isn’t only irritating, it can be dangerous. Quiet racks use acoustic foam or noise reducing designed systems to bring that roar down to a whisper, and dissipate excessive heat produced by servers, disk drives and controllers by up to 7.2KW.

Seismic Server Racks
Seismic server racks are designed to withstand shock from earthquakes. Whether Zone 1, or Zone 4, seismic racks are built to ensure your equipment stays operational during a seismic event. NEBS (Network Equipment-Building Systems) cabinets go through months of rigorous testing to obtain seismic certification in order to meet EC&M building code requirements. Typical racks are engineered with extra cross bracing. These racks are bolted to the floor to prevent tipping.

Cable Network Racks
If you have a network, you probably have a lot of cable bundles. Most server cabinets don’t leave much room for those large bundles, forcing you to rearrange your equipment to accommodate them. Cable network racks have adjustable vertical rails, allowing them to slide left or right - forward and backwards. These cabinets are generally wider than most server cabinets and have widths from 19” to 28”, allowing cables to drop down one or both sides of the cabinet.

NEMA Certified Enclosures
The National Electrical Manufacturer Association (NEMA) uses a standard testing system to define the type of environment where an electrical enclosure can be used. Whether for indoor or outdoor use, hazardous environments and even submerged under water – NEMA certified enclosures are built to keep equipment safe no matter what Mother Nature throws at them.

Network Switch Cabinets
The network switch rack is a wide-bodied server rack designed to support large, modular network switches while allowing for proper airflow. With a wider cabinet footprint, these monstrosities provide extra space on either side of your rackmounted equipment for cable management and side-to-side airflow solutions.

What kind of equipment can you install in a rack?

IT Production Equipment

IT production equipment is the servers, storage, network switches, routers, telecommunications hardware and other devices

that fulfill the primary purpose of the IT installation. (Racks also have applications that may not employ typical IT equipment,

such as manufacturing, but the same general principles apply.)

Racks are designed to hold all standard 19-inch rack-mountable equipment, as long as it isn’t too deep for the cabinet or

too high to fit in the available rack spaces. The equipment often includes removable mounting brackets or “ears” that fasten

to the vertical rack rails with screws. Heavier equipment may also include horizontal rails or shelves that mount in the rack to

provide extra support. If the equipment isn’t made for rack installation, you can install a rack shelf to hold it. Just make sure

the equipment isn’t too big or heavy for the shelf.

IT Infrastructure and Rack Accessories

Racks also accommodate IT infrastructure and rack accessories that support the operation of the production equipment. This

includes equipment like UPS systems (uninterruptible power supplies), PDUs, cable managers, KVM switches, patch panels

and shelves. Although most equipment is designed to fit in standard rack spaces, vertical PDUs and cable managers mount

to vertical rails without using any rack spaces. Equipment that installs this way is referred to as 0U (“zero U”). 

How do you choose the right rack  size?


The height of the rack is one of the most important considerations because it determines how many rack spaces are

available for your equipment. In fact, the height of the rack is expressed in the number of available rack spaces. (You can

also find the external measurements to make sure the rack will fit through the doors in your facility.) Common heights for

floor-standing racks and rack enclosures are 42U, 45U and 48U, with custom sizes up to 58U available for some high-density

data center applications. You may also wish to leave extra space for horizontal cable managers, future expansion or other

purposes, so keep that in mind when determining the height.


Since the width of the rack’s mounting rails and the rack equipment itself is standardized, that part is simple—just make sure

your equipment and your rack both follow the EIA-310-E standard. But you also need to consider the external width of the

rack. The standard width for rack enclosures is 24 inches or 600 mm, which corresponds to the standard for removable floor

tiles in a raised-floor data center. Extra-wide rack enclosures (30 inches or 750 mm) are also available, with or without extra

depth. Enclosures with extra width have side channels that accommodate PDUs, high-density cabling and cable managers

without obstructing airflow. This is especially helpful for network switches that have side-to-side airflow and forward-facing

ports. Extra-wide rack enclosures may also have modified vertical mounting rails that include built-in cable channels. Some

extra-wide racks can even be customized with extra rack spaces at the sides to fit as much equipment as possible.


The rack’s depth is important because you need to make sure it will be deep enough for your equipment, including any

cabling that extends past the equipment cabinet. You can usually adjust the depth of the vertical mounting rails in a fourpost

rack or rack enclosure, but only within certain limits. The standard depth for a rack enclosure is around 42 inches,

but you can get extra-deep (48 inches) rack enclosures for deeper servers and blade chassis. The extra depth ensures that

there’s enough room for cabling, PDUs, cable managers and other accessories without blocking airflow or compromising

serviceability. There are also racks that are shallower than the standard depth to save space. These are available as middepth

(36 inches) and shallow-depth (32 inches) enclosures. Wall-mount rack cabinets are usually shallower than their floorstanding

counterparts, with usable mounting depths around 12, 16, 20 or 32 inches.

Load Rating

The load rating (or weight capacity) of the rack is how much weight it can safely support. Remember that you also need to

make sure that your facility’s floor can support the weight of the rack and any equipment installed inside it. If you’re installing

a wall-mount rack, both the wall and the fasteners need to be able to support the combined weight. Racks usually list two

different load ratings: a stationary/static load rating for when the rack is installed in place and a rolling/dynamic load rating

for when the rack is rolled from place to place on its casters. (The stationary/static and rolling/dynamic load ratings may be

equal if the rack has heavy-duty casters.) 

Where can you find more advice if you need it ?