Which characteristic defines rack servers?

Rack servers are specifically designed to be mounted in a standard server rack, which allows for a space-efficient configuration. This design maximizes the use of available physical space in data centers, enabling organizations to optimize their hardware deployment without taking up excessive floor space. The stackable nature of rack servers means that they can be arranged vertically within the rack, providing organized access and managing cable connections effectively.

The characteristic of being space-efficient is crucial for data centers, where maximizing real estate while minimizing power and cooling costs is a priority. This design also facilitates easier maintenance and upgrades, as servers can be rapidly accessed and swapped due to their standardized dimensions.

In contrast, other characteristics such as portability would suggest a design intended for easy transport and setup, which is not the primary focus of rack servers. Similarly, standalone operation ability implies that the server could function independently without the need to be integrated into a larger system of racks, which does not align with the typical use case for rack servers. Lastly, limited connectivity options would not accurately describe rack servers, as they generally offer a wide range of connectivity options to support diverse networking and storage needs.