What is the X in X-mas?
system, design, hardware, software
(RAS) Three key attributes of a computing system design. See reliability, availability, and serviceability.
The term "RAS" is fairly common in the computing industry (particularly computers and storage) as computing becomes more fundamental. For example, a vehicle may depend on dozens of computers, and the consequences of the failure can be significant (e.g., an ambulance's engine won't start).