What kind of servers are considered non-common according to the text?

The distinction of "non-common" servers typically refers to those varieties that are less frequently utilized in standard IT environments compared to more conventional deployments like rack and tower servers. Blade and composable servers fit this classification because they represent advanced, modular designs that are aimed primarily at highly dynamic or specialized computing needs.

Blade servers are designed to maximize space efficiency and are often used in environments where high-density computing is paramount. Composable servers take this concept further by allowing IT resources to be assembled and disassembled in a software-defined manner, catering to specific workloads while optimizing resources.

In contrast, rack and tower servers are widely implemented and align with traditional server deployment strategies. Similarly, SAN arrays and containers, although useful, are often classified in ways that don’t focus specifically on the server form factor. Tower and mainframe servers also lean towards traditional setups seen in many businesses today.

Thus, blade and composable servers are correctly identified as non-common because of their specialized applications and advanced technologies, which are not as prevalent in typical enterprise infrastructures.