Rack Unit

A rack unit (abbreviated as U or RU) is a standardized unit of measure for the height of equipment designed to mount in a 19-inch rack or a similar standardized enclosure [8]. Equal to 1.75 inches (44.45 mm), one rack unit defines the vertical space between the mounting holes on the rack's vertical rails [6]. This measurement is the fundamental building block for the globally standardized 19-inch rack frame, which is used for mounting electronic equipment modules such as servers, network hardware, industrial controls, and audiovisual gear [1][3]. The rack unit system enables the precise vertical dimensioning of equipment, ensuring that devices from different manufacturers can be securely mounted and organized within the same enclosure [2]. This standardization is critical for data centers, telecommunications facilities, and broadcast environments, where efficient use of physical space and reliable hardware interoperability are paramount [7]. The specification for the standard rack, including the rack unit dimension, is formally defined by standards such as the EIA-310, which details the rack's mounting hole spacing and overall dimensions [4]. International equivalents include the IEC 60297 and DIN 41494 standards, which maintain consistency in rack unit sizing to preserve global hardware interchangeability [2]. A piece of equipment's size is described by how many rack units it occupies in height; for example, a 1U server is 1.75 inches tall, a 2U server is 3.5 inches tall, and so on [8]. The rack itself is characterized by its width of 19 inches (482.6 mm) between the mounting rails, with the total height of a rack enclosure typically expressed as a multiple of rack units, such as 42U [1]. Beyond basic dimensions, broader standards like the IEC 61587 series provide guidance for ancillary requirements including cooling, electromagnetic compatibility (EMC), and seismic resilience for rack-mounted equipment [5]. The primary application of the rack unit system is in information technology and communications infrastructure, where it allows for the systematic organization and physical securing of critical hardware within server racks [7]. This standardization is significant because it underpins the design, manufacturing, and deployment of virtually all enterprise and data center computing equipment, creating a universal ecosystem for hardware integration [2]. The rack unit's modern relevance extends beyond traditional IT, finding essential use in professional audio-visual installations, scientific instrumentation, and industrial control systems, wherever modular, reliable, and space-efficient equipment mounting is required [1][6]. By providing a consistent frame of reference for equipment height, the rack unit facilitates efficient capacity planning, thermal management, and cable organization within technical enclosures, making it an indispensable component of contemporary digital infrastructure [7].

Overview

A rack unit, universally abbreviated as U or RU, is the fundamental standardized unit of measure for the vertical space within equipment racks, serving as the cornerstone for the design, manufacturing, and deployment of electronic hardware across the information technology, telecommunications, and industrial sectors [14]. This unit of measure is intrinsically linked to the 19-inch rack, a globally standardized frame or enclosure that provides the structural foundation for mounting a vast array of equipment, including servers, network switches, routers, power distribution units, industrial control systems, and professional audiovisual gear [13]. The symbiotic relationship between the rack unit and the 19-inch rack framework enables unprecedented levels of organization, density, and physical security for critical infrastructure, forming the physical backbone of data centers, network operation centers, and equipment rooms worldwide [13].

Standardization and Interchangeability

The primary function of the rack unit is to ensure hardware interchangeability and compatibility across international manufacturers and brands. By adhering to this common dimensional standard, equipment producers can design their chassis with the confidence that they will physically fit into any compliant rack, regardless of the rack's manufacturer or geographic origin [13]. This universal compatibility eliminates vendor lock-in at the physical layer, allowing data center operators and network engineers to mix and match hardware from diverse suppliers such as Dell, Hewlett Packard Enterprise, Cisco, Juniper, and countless others within the same rack enclosure. The standard governs not only the vertical height but also the horizontal width and mounting hole patterns. The nominal 19-inch rack width refers to the distance between the two vertical mounting rails, which is standardized at 19 inches (482.6 mm) [13]. Equipment faceplates are designed to be slightly less than 19 inches wide to allow for clearance, while the mounting holes on the equipment's ears align precisely with the threaded or square holes on the rack's vertical rails. This holistic standardization of width, height, and hole spacing is what creates a truly modular ecosystem for hardware deployment.

Calculation and Application

The value of one rack unit (1U) is defined as 1.75 inches (44.45 millimeters) [14]. This measurement is used to specify the height of any rack-mountable device. The height of such equipment is expressed as a multiple of this unit. For example:

A 1U server is approximately 1.75 inches (44.45 mm) tall
A 2U server is approximately 3.5 inches (88.9 mm) tall
A 4U chassis is approximately 7 inches (177.8 mm) tall

The total capacity of a rack enclosure is similarly described by the sum of its available rack units. Common full-size rack heights include 42U and 45U, which equate to internal vertical spaces of approximately 73.5 inches (1866.9 mm) and 78.75 inches (2000.25 mm), respectively [13]. When planning a rack layout, administrators must sum the "U" values of all devices to be installed, including necessary ancillary components like shelf units, blanking panels, and cable management arms, ensuring the total does not exceed the rack's physical capacity. This allows for precise capacity planning and optimal utilization of expensive data center floor space, where power density and cooling efficiency are directly tied to how effectively vertical space is managed.

Evolution and Derivative Standards

The 19-inch rack format, and by extension the rack unit, originated in early telephone and switching equipment industries in the early 20th century. Its adoption by the computing and networking industries solidified its position as a de facto global standard. While the 19-inch rack is predominant, derivative standards have emerged for specific applications requiring different form factors. A prominent example is the 23-inch rack, occasionally used in telecommunications and some European contexts. The principle of the rack unit remains consistent, with 1U still equal to 1.75 inches, but the width between the mounting rails is increased. Furthermore, the growth of hyperscale computing has led to the development of open rack standards like the Open Compute Project (OCP), which may define alternative dimensions for extreme density and efficiency. However, even these newer frameworks often maintain a logical unit of vertical measurement analogous to the traditional rack unit to preserve concepts of modularity and height aggregation.

Importance in Infrastructure Design

The rack unit system is critical for more than just physical mounting; it is a key planning metric for thermal management, power delivery, and cable infrastructure. Data center design relies on per-rack power budgets (often measured in kilowatts per rack) and cooling capacity, which are directly influenced by the number and type of U-sized devices installed. High-density 1U servers packed into a rack will generate more heat and require more power and cooling than a rack populated with fewer, larger 4U storage arrays. As noted earlier, the vertical space between mounting holes on the rack's vertical rails is defined by this standard, which in turn dictates the placement of equipment and the organization of associated cabling. Proper use of the space, including the installation of blanking panels in unused U positions, is a best practice for maintaining efficient airflow and preventing hot and cold air mixing within the enclosure. Thus, the rack unit transcends its role as a simple measurement and becomes a fundamental unit of account for data center resource allocation, capacity planning, and operational efficiency, enabling the scalable and orderly growth of modern digital infrastructure [13].

History

Early Precedents and the 19-inch Rack Standard

The concept of standardized equipment mounting has its roots in early 20th-century telephony and radio engineering. While the specific term "rack unit" would not be formalized until later, the need for organized, interchangeable hardware mounting became apparent with the proliferation of complex electronic systems. The foundational standard, the 19-inch rack, emerged from the telecommunications industry. Its dimensions were likely codified by the American engineering community, with early references appearing in Bell System practices and other telephony standards. The width of 19 inches (482.6 mm) between the mounting rails became a de facto standard for mounting panels and chassis, facilitating the organization of relay banks, test equipment, and early switching gear in central offices [14]. This established the critical principle of interchangeability, allowing hardware from different manufacturers to be installed side-by-side within the same framework, a concept that would become the cornerstone of modern data centers and equipment rooms [14].

Formalization of the Rack Unit (U)

The evolution from a standardized rack width to a standardized vertical increment—the rack unit—was a subsequent and equally critical development. The rack unit, abbreviated as "U" or "RU," was defined to standardize the vertical space occupied by equipment. As noted earlier, one rack unit defines the vertical space between the mounting holes on a rack's vertical rails. This precise vertical metric allowed for the reliable planning of space and airflow within equipment enclosures. The formalization of the U dimension is intrinsically linked to the Electronic Industries Alliance (EIA) standard EIA-310. This standard, which codified the specifications for racks, panels, and associated hardware, provided the definitive technical blueprint for the 19-inch rack, including the precise definition of the rack unit [14]. The EIA-310 standard ensured that a piece of equipment designated as 1U by one manufacturer would physically fit into the same space as a 1U device from any other compliant manufacturer, enabling true global hardware interoperability [14].

Adoption and Expansion Across Industries

Following its standardization, the rack unit system saw rapid adoption beyond its telecommunication origins. The late 20th century, driven by the computer revolution and the rise of corporate data networks, propelled the 19-inch rack into information technology. Servers, network switches, routers, and storage arrays were increasingly designed in rack-mount form factors, measured in precise increments of U [14]. This period also saw the rack unit's adoption into professional audio-visual and broadcast industries. Equipment such as amplifiers, mixing consoles, signal processors, and broadcast routers were packaged in rack-mountable enclosures, allowing for the creation of integrated, space-efficient production and sound reinforcement systems [14]. Manufacturers like RDL® produced studio-quality electronic equipment, such as half-rack width modules, designed to be 1RU in height, demonstrating the standard's flexibility for specialized applications [15]. The proliferation of the standard across these diverse fields—data centers, telecommunications, and audio-visual production—solidified its status as a universal engineering practice [14].

The original EIA-310 standard has been superseded and refined by newer specifications to address evolving technical requirements. In the United States, the Telecommunications Industry Association (TIA) published the ANSI/TIA-310-E standard, which continued to define cabinet, rack, and panel specifications. Internationally, the International Electrotechnical Commission (IEC) standard 60297 provides a comprehensive framework for mechanical structures, detailing dimensions for the 19-inch rack series. These international standards govern not only the basic width and U height but also critical details such as:

The precise spacing and diameter of mounting holes
Tolerances for rail dimensions
Specifications for rack depth and mounting flange profiles
Requirements for grounding and structural integrity

The technical overview of international 19-inch cabinet standards encompasses these detailed specifications, ensuring compatibility across global supply chains. The rack unit's definition remains central to these documents, enabling the design of high-density systems. For example, the common 42U rack, a staple in data centers, represents the total available vertical mounting space as a sum of rack units, allowing planners to maximize equipment density within floor space and power delivery constraints. Building on the concept discussed above, this capacity planning is fundamental to modern infrastructure design.

The Rack Unit in Contemporary Infrastructure

Today, the rack unit is an indispensable metric in the design and operation of critical technical infrastructure. Its application extends into industrial automation, where programmable logic controllers (PLCs) and control systems are rack-mounted, and into scientific instrumentation. The standard has also adapted to accommodate deeper equipment, with common rack depths now including 600mm, 800mm, 1000mm, and 1200mm to house modern servers with extensive cable management and cooling requirements. The principle of interchangeability, established decades ago, remains paramount, allowing organizations to integrate hardware from a global marketplace of vendors seamlessly. The history of the rack unit is, therefore, a history of pragmatic standardization—a simple measurement that evolved from telephony practice into a universal language for physical hardware deployment, underpinning the interconnected digital world. Its continued relevance is a testament to the enduring value of well-conceived, open engineering standards.

Description

A rack unit (abbreviated as U or RU) is a standardized unit of measure that defines the vertical space available for equipment within a standardized mounting frame or enclosure [1][6]. The primary purpose of this unit is to provide a universal dimensional framework that ensures hardware from different manufacturers can be mounted and interchanged within the same infrastructure [2]. This standardization is foundational to the design and deployment of equipment across multiple critical industries.

Technical Definition and Dimensional Basis

The rack unit is precisely defined as 1.75 inches (44.45 mm) in height [1]. This measurement is not arbitrary but is derived from the vertical spacing between the mounting holes on the vertical rails of a standardized 19-inch rack [1]. The rack unit serves as the fundamental building block for specifying the physical size of rack-mountable equipment. For instance, a device described as 1U occupies a single rack unit of vertical space, while a 2U device occupies two units, and so on [1]. The total height of a rack enclosure itself is expressed as a multiple of this unit, with common sizes including 42U and 48U, indicating the maximum number of rack units of equipment it can accommodate [1]. The dimensional consistency of the rack unit is governed by formal specifications. The RU size is explicitly based on the standard rack specification defined in the Electronic Industries Alliance (EIA) specification EIA-310 [6]. This specification, along with others, ensures that the 1.75-inch unit is maintained globally, allowing for the predictable layout and maximum density of equipment within data centers, network closets, and broadcast facilities.

Associated Rack Standards and Hole Spacing

The rack unit is intrinsically linked to the 19-inch rack standard, which defines the width between the two vertical mounting rails [2]. The standard specifies that the distance between the inner faces of these two rails is 17.75 inches (450.85 mm), providing the width constraint for all mounted equipment [2]. This 19-inch rack arrangement, characterized by its 450 mm rail spacing, has become ubiquitous in telecommunications, computing, audio, video, and entertainment industries [4]. It is important to note that other standards exist, such as the historical 23-inch standard used by Western Electric, which features holes spaced on 1-inch (25.4 mm) centers, but the 19-inch standard dominates the global market [4]. The mounting of equipment is facilitated by specific hole patterns on the rack rails. A common and critical pattern involves groups of three holes, with the holes within each group spaced at 0.625 inches (15.875 mm) apart, center-to-center [2]. These three-hole groups are then repeated vertically with a spacing of 1.75 inches (44.45 mm) from the center of the first hole in one group to the center of the first hole in the next group [2]. This 1.75-inch spacing between hole groups directly corresponds to one rack unit and is the mechanical basis for securing equipment of standard U heights.

International Standardization Frameworks

The standardization of rack units and 19-inch racks is not governed by a single entity but is encapsulated within several key international and national standards. This multi-standard approach ensures global interoperability.

The ANSI/EIA RS-310-D standard is a pivotal American specification that defines the dimensions for racks, panels, and associated equipment [2]. It formalizes the 19-inch width and the rack unit measurements that are widely adopted.
The IEC 60297 series of standards, developed by the International Electrotechnical Commission, provides the international counterpart [2]. For example, IEC 60297-3-105:2008 specifies the detailed dimensions for 1U high chassis that are designed to be mounted into racks and cabinets compliant with the overarching IEC 60297-3-100 standard [5]. This illustrates how standards define not just the rack, but also the precise form factors of the equipment that populate it.
The DIN 41494 standard, originating from Germany's Deutsches Institut für Normung, is another crucial specification, particularly influential in the European market [2]. It covers similar mechanical dimensions, ensuring compatibility across different regulatory environments. The existence and harmonization of these standards—ANSI/EIA, IEC, and DIN—are what enable the true interchangeability of hardware across international brands and geographical borders [2]. A server chassis designed to the EIA-310 specification in the United States will fit seamlessly into a rack built to the IEC 60297 standard in Europe or the DIN 41494 standard in Germany, provided the rack unit height and 19-inch width are adhered to.

Practical Application and Equipment Design

In practical terms, the rack unit system dictates the external "envelope" dimensions of equipment. Design engineers use the rack unit as a constraint when developing servers, switches, patch panels, power distribution units (PDUs), and audio mixers. The height of the equipment's front panel or chassis is designed to be a multiple of 1.75 inches, minus small tolerances to allow for fit and mounting ears [1]. The standardization extends to the depth of equipment and racks, though depth is more variable than height or width. While the front-mounting width and vertical spacing are fixed, racks and cabinets come in various depths (e.g., 600mm, 800mm, 1000mm, 1200mm) to accommodate equipment with different depth requirements, from shallow network switches to deep storage servers [2]. The rack unit system does not standardize depth, but the overall cabinet standards often define depth profiles and related clearances. The universal adoption of this system allows data center operators and network engineers to plan capacity with precision. They can calculate total power requirements, cooling load, and weight distribution based on the known U-height of each piece of equipment. This level of predictability is essential for efficient and reliable infrastructure management. The rack unit, therefore, is more than a simple measurement; it is a critical component of a global engineering language that enables the organized, dense, and scalable deployment of the electronic equipment that powers modern digital infrastructure.

Significance

The rack unit (U) and the 19-inch rack framework it defines constitute a foundational technical standard that enables the modern, high-density infrastructure underpinning the digital economy. Its significance extends far beyond a simple measurement, serving as a critical enabler of interoperability, scalability, and operational efficiency across multiple critical industries. The system's enduring relevance is a testament to its successful balance of rigid specification for compatibility and sufficient flexibility to accommodate decades of technological evolution.

### Enabler of Global Infrastructure Interoperability

The most profound significance of the rack unit system lies in its role as a universal hardware language. By providing a strictly defined dimensional framework—centered on the 19-inch (482.6 mm) panel width and the 1.75-inch (44.45 mm) vertical unit—it guarantees that equipment from any manufacturer worldwide can be physically integrated into a shared infrastructure [13][17]. This interchangeability eliminates vendor lock-in at the physical layer, allowing data center operators, broadcast studios, and telecommunications providers to select best-in-class hardware based on performance, cost, or feature set without concern for mounting compatibility [20]. The standard ensures that mounting holes on equipment align precisely with the threaded holes or square openings on the rack's vertical rails, which are spaced 450 mm apart [16][10]. This mechanical compatibility is so complete that a server chassis designed in the United States can be installed seamlessly into a rack in a European or Asian facility, a non-trivial achievement in global engineering standardization.

### Critical Role in Data Center Design and Efficiency

In data centers, the rack unit is the fundamental metric for capacity planning, power distribution, and cooling design. The total height of server racks is expressed as a multiple of U, with common sizes being 42U (approximately 73.5 inches) and the larger 48U (84 inches) used for high-density applications [13]. This standardization allows for precise calculation of:

Power Density: Power requirements are often planned on a per-U or per-rack basis, with high-performance computing cabinets consuming 20kW or more.
Cooling Capacity: HVAC systems are designed to handle the heat output per rack, which is directly related to the number and type of U-sized devices installed.
Physical Space Optimization: The ability to mix and match 1U, 2U, 4U, and other form-factor servers within the same enclosure allows operators to tailor storage, compute, and networking capacity to specific workloads without wasting vertical space [22]. Furthermore, the consistent external frame dimensions, particularly the 450 mm rail spacing, enable innovative and space-saving layouts. For instance, 42U racks can be configured in side-by-side, back-to-back, or even T-shaped arrangements without requiring custom intermediate frames, maximizing floor space utilization in expensive colocation facilities [21].

### Backbone of Telecommunications and Networking

The 19-inch rack format originated in the telephone industry of the early 20th century and remains indispensable to modern telecommunications and networking [16]. It provides the structured physical layer for mounting:

Core and edge routers
Network switches
Fiber optic termination panels
Voice over IP (VoIP) gateways and session border controllers
Power over Ethernet (PoE) injectors and media converters

The standard's scalability allows network architects to design centralized wiring closets, main distribution frames (MDFs), and internet exchange points where equipment from dozens of competing vendors must coexist and interconnect. The predictable panel width of 19 inches ensures that cable management, including horizontal and vertical cable managers, can be uniformly applied, maintaining proper bend radius and organization for thousands of copper and fiber patch cords [20].

### Foundation for Professional Audio-Visual Systems

Beyond IT and telecom, the rack unit system is the organizational backbone of professional audio, video, and broadcast production environments [18]. It standardizes the installation of:

Audio mixing consoles and digital audio workstations (DAWs)
Power amplifiers and audio signal processors
Video switchers, production servers, and graphics generators
Broadcast monitors and patchbay panels

This allows touring sound companies, fixed-installation theaters, and television broadcast trucks to pre-build and test systems in standardized racks before deployment. The ability to quickly swap a faulty amplifier or processor with a unit from a different manufacturer, knowing it will fit the existing rack space and faceplate, is critical for live events where downtime is unacceptable.

### Limitations and Adaptations

While the standard is overwhelmingly successful, its significance is also clarified by its defined limitations, which have spurred further innovation. As noted earlier, the standard primarily governs front-panel width and vertical spacing, not depth or environmental protection. Equipment depth can vary significantly, requiring racks to be manufactured in various depths (e.g., 600mm, 800mm, 1000mm, 1200mm) to accommodate everything from shallow network switches to deep storage arrays [14]. Furthermore, standard open-frame racks offer limited environmental protection, often necessitating enclosed cabinets with integrated cooling, air filtration, and electromagnetic interference (EMI) shielding for deployments in harsh industrial or military settings [19]. The rack unit's endurance as a standard for over half a century, adapting from electromechanical telephone switches to hyperscale cloud servers, underscores its fundamental utility. It provides just enough constraint to ensure global interoperability while offering ample freedom for engineering innovation within the defined form factor. This combination has made the humble "U" an indispensable unit of measure in building the physical infrastructure of the interconnected world.

Applications and Uses

The rack unit (U) system, built upon the foundational 19-inch rack standard, is indispensable for organizing and managing electronic hardware across a vast spectrum of industries [18]. Its universal dimensional framework enables the precise planning, deployment, and scaling of critical infrastructure by providing a predictable and interoperable form factor for countless devices.

Data Center and Enterprise Computing

In data centers and enterprise server rooms, the rack unit is the fundamental metric for capacity planning, space allocation, and thermal management. The total height of a rack enclosure, expressed as a multiple of rack units, directly determines how much equipment can be housed in a given footprint [7]. Standard full-height racks are typically 42U (approximately 73.5 inches or 1,866.9 mm tall), while half-height racks are often 22U or 24U [21]. For higher-density applications, such as hyper-scale data centers or telecommunications hubs, enclosures can extend to 45U or 48U (approximately 84 inches tall) to maximize the number of devices per square foot of floor space. The standardization of the 19-inch width and U-height allows for the efficient co-location of diverse hardware from multiple manufacturers within a single rack [17]. A typical configuration might include:

1U and 2U rack-mounted servers for general computing
4U chassis for high-performance computing or storage arrays with numerous hard drives
1U or 2U network switches and routers, often mounted at the top of the rack for easier cable management
1U or 2U power distribution units (PDUs) and keyboard-video-mouse (KVM) switches mounted at the rear

The depth of these enclosures is also standardized to accommodate varying equipment, with common depths including 600mm, 800mm, 1000mm, and 1200mm [22]. This ensures that everything from shallow network switches to deep storage servers and blade chassis can be securely housed and organized.

Telecommunications and Networking

The 19-inch rack has its historical roots in the telecommunications industry, where it was adopted to organize relay banks, test equipment, and early switching gear in central offices [19]. This legacy continues today, as the rack unit remains the primary standard for mounting modern telecommunications equipment. Building on the concept of interchangeability discussed earlier, this allows service providers to deploy hardware from different vendors—such as optical line terminals (OLTs), multiplexers, channel banks, and fiber distribution panels—into the same rack infrastructure seamlessly [18]. The standard width ensures that devices, which can be up to 280 mm wide including their mounting brackets, fit within the 450 mm spaced rails of the rack [17]. For narrower equipment, enclosure adapters are available to bring two half-width (9.5-inch) units side by side to fill a standard 19-inch width, optimizing space utilization for smaller modules [8].

Audio-Visual and Broadcast Production

Beyond IT and telecom, the rack unit is a critical standard in professional audio, video, and broadcast environments. In these fields, the consistent form factor allows for the integration of diverse equipment into portable road cases and fixed installation racks. Common rack-mounted A/V equipment includes:

Audio mixers, amplifiers, and digital signal processors (DSPs)
Video switchers, distribution amplifiers, and format converters
Broadcast servers, recording decks, and monitor displays
Power conditioners and equipment for lighting control

The use of standard rack units allows production companies and broadcast facilities to design systems with predictable dimensions, ensuring that gear from audio, video, and control system manufacturers can be integrated into a cohesive and transportable package. The standard 19-inch width is ubiquitous in these industries, facilitating the global interoperability of professional equipment [18].

Industrial, Military, and Test & Measurement

The benefits of standardization extend into industrial control, military communications, and scientific instrumentation. In industrial settings, programmable logic controllers (PLCs), human-machine interfaces (HMIs), and network gateways are often housed in 19-inch racks for protection and organization within factory environments. For military communications, the evolution of rack enclosures has emphasized ruggedization and modularity, allowing for the rapid reconfiguration of field-deployable systems while maintaining compatibility with standard rack-unit dimensions [19]. In laboratory and test environments, the rack unit system organizes sensitive measurement equipment—such as oscilloscopes, signal generators, spectrum analyzers, and power supplies—into standardized benchtop or floor-standing racks. This organization simplifies system integration, cable management, and maintenance for complex test setups.

Space Planning and Optimization

Knowing what "U" stands for is critical for infrastructure planning because it translates physical equipment size into a uniform measure for vertical space [7]. Data center managers use this to calculate:

Power density per rack (watts per U or per rack)
Cooling requirements based on heat load and equipment layout
Cable management pathways and clearances
Floor load capacity based on aggregated equipment weight per rack

The consistent external frame dimensions, particularly the 450 mm rail spacing, enable innovative and space-saving layouts, such as arranging racks in hot aisle/cold aisle configurations to improve cooling efficiency. The ability to mix and match 1U, 2U, 4U, and other devices within the same rack allows for the optimal use of every vertical unit of space, delaying the need for costly data center expansion.