IBM System z (officially "IBM z Systems") is a family name used by IBM for all of its mainframe computers.In 2000, IBM renamed the existing System/390 to IBM eServer zSeries with the e depicted in IBM's red trademarked symbol, but because no specific machine names were changed for System/390, the zSeries in common use refers only to the z900 and z990 generations of mainframes.In April 2006, with another generation of products, the official family was changed to IBM System z, which now includes both older IBM eServer zSeries, the IBM System z9 models, the IBM System z10 models, and the newer IBM zEnterprise.The zSeries, System z and zEnterprise families were named for their availability – z stands for zero downtime.