Linux® on the Mainframe

11.2. The zSeries hardware availability

At the turn of the century when IBM reorganized its disparate processor divisions into the eServer brand, each of the four server teams got to choose a letter to precede the word “Series.” The old S/390 division chose the letter “z” for near-zero downtime, to reflect its focus on a design for continuous availability of the processors.

The design of the zSeries processor takes into account single points of failure in many ways. All levels of memory have a type of ECC (error correction code) that ensures that single-bit (often multiple-bit) failures are corrected “on the fly.” The instruction processing unit itself has two identical sets of logic executing every instruction. If the results do not agree, then ...