The phrase was originally used by IBM as a term to describe the robustness of their mainframe computers.
[1][2] Computers designed with higher levels of RAS have many features that protect data integrity and help them stay available for long periods of time without failure.
For example, a server may run forever and so have ideal availability, but may be unreliable, with frequent data corruption.
A successfully corrected intermittent fault can also be reported to the operating system (OS) to provide information for predictive failure analysis.
Example hardware features for improving RAS include the following, listed by subsystem: Fault-tolerant designs extended the idea by making RAS to be the defining feature of their computers for applications like stock market exchanges or air traffic control, where system crashes would be catastrophic.