What is the primary advantage of mainframe computers?

The primary advantage of mainframe computers being the ability to allow modifications to system capacity while the system is in use highlights their robustness and flexibility in handling significant workloads. Mainframes are designed to support large-scale computing tasks and can efficiently adjust resource allocation, such as processing power and memory, without needing to shut down operations. This is particularly important for organizations that require high availability and cannot afford downtime.

In high-demand environments, such as banking, telecommunications, and large-scale transaction processing, maintaining continuous operation is crucial. The capacity to upscale or downscale resources on-the-fly ensures that mainframes can meet peak loads while optimizing performance.

Other reasons for selecting this option include the emphasis on the mainframe's architecture, which allows for significant input/output capabilities, and enterprise-level reliability that is not typically matched by smaller systems. This distinguishes mainframes from personal computers, which cannot handle similar modifications while the system is operational.