When UNPK Broke – Diagnosing an IBM Mainframe Hardware Failure

Podcast: IT Horror Stories with Jack Smith · Jack Smith

Opublikowano: 2026-09-21

Texas, 1978. Robert was working at a cotton co-op running what may have been one of the world's earliest online auction systems. Farmers received punch cards representing their bales of cotton - occasionally complete with enough stray cotton fibres to jam the card readers - while buyers placed bids remotely using leased IBM 3270 terminals and acoustic coupler modems. After an upgrade, the mainframe refused to come back properly. An IPL produced a corrupted device address before dropping the machine into a hard wait. Single-cycling the processor indicated that an UNPK (Unpack) instruction was producing the wrong output from...