mainframe

Definitions

1. A large, centralised computer built for extremely high transaction volumes, massive input and output throughput, and near-continuous availability. The modern lineage begins with IBM's System/360 in 1964, whose compatible family of machines established the architecture that today's IBM Z systems still run, so programs written decades ago can execute unchanged. Mainframes typically run z/OS or Linux, with transaction monitors such as CICS, databases such as Db2 and IMS, batch jobs described in JCL, and large amounts of COBOL. Reliability comes from redundant hardware, hot-swappable components, and clustering through Parallel Sysplex. Despite decades of predicted decline, mainframes remain central to banking, insurance, government, and airline reservations, and IBM has long claimed that most of the world's card transactions touch one. The practical challenges now are cost, licensing tied to processing capacity, and a shrinking pool of engineers who know the platform.

   In plain English: A very large, very reliable computer used by banks and big companies — they've been 'dying' for 40 years but still run most of the world's financial transactions.

   Example: The bank's core ledger still runs on a mainframe from the 90s, and the two people who understand the COBOL code are both approaching retirement.

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