The IBM zEnterprise® system introduced a new and innovative redundant array of independent memory (RAIM) subsystem design as a standard feature on all zEnterprise servers. It protects the server from single-channel errors such as sudden control, bus, buffer, and massive dynamic RAM (DRAM) failures, thus achieving the highest System z® memory availability. This system also introduced innovations such as DRAM and channel marking, as well as a novel dynamic cyclic redundancy code channel marking. This paper describes this RAIM subsystem and other reliability, availability, and serviceability features, including automatic channel error recovery; data and clock interface lane calibration, recovery, and repair; intermittent lane sparing; and specialty engines for maintenance, periodic calibration, power, and power-on controls.