mainframe
n.a very large and powerful computer used by big companies or governments to handle huge amounts of data.
n.a high-performance computer system designed for high-volume data processing and critical applications requiring extreme reliability.
“The bank uses a mainframe to process millions of transactions every day.”
“While many companies have moved to the cloud, some still rely on a central mainframe for their most sensitive financial records.”
“The transition from legacy mainframe architecture to distributed cloud systems remains a significant technical challenge for many established government agencies.”
Often used as a modifier before other nouns, such as 'mainframe computer' or 'mainframe system'.
From main + frame.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.