Y2K

Y2K, short for Year 2000, also known as the Millennium Bug, was a computer-science and information-technology issue tied to how dates were stored in software and embedded systems. Many programs represented a year with two digits, such as "98" for 1998. When the year 2000 arrived, those systems could interpret "00" as 1900, potentially causing incorrect date calculations, program crashes, or data corruption across financial, utility, transportation, and government networks.

The problem grew from a decades-long practice to save memory and storage during earlier computer development; as the year 2000 approached, the risk spread to a wide range of systems, including legacy mainframes, databases, and embedded controllers in devices such as industrial equipment and consumer electronics. Preparing for the rollover involved inventorying systems, correcting date handling, adding four-digit years, and testing date arithmetic and leap-year logic across both software and firmware.

Government agencies, businesses, and international organizations undertook extensive remediation, audits, and contingency planning. Efforts included code fixes, system replacements, data-cleansing, and disaster-recovery planning, as well as public- and private-sector awareness campaigns. Estimates of total costs varied widely, ranging from tens of billions to multiple hundreds of billions of dollars. Many organizations conducted extensive testing and third-party verification.

When January 1, 2000 arrived, the rollover proceeded with few major failures, and most systems behaved as intended. The event is commonly considered a success of risk management and coordinated remediation, despite some minor glitches. The Y2K episode influenced software engineering practices, emphasizing robust date handling, inventory and risk assessment, and improved project management for large-scale IT modernization.