(IBM had an earlier system called RAMAC. See RAMAC (original).)
RAMAC (pronounced RAY-mac; IBM does not spell out the initials) is a multiple-disk storage subsystem from IBM that emphasizes fault-tolerance and is intended for large enterprises. IBM claims that its RAMAC product family "provides the highest data availability of any DASD subsytem." The RAMAC product family uses redundant array of independent disks technology (RAID) - in particular, the RAID-5 storage technique. RAMAC also includes redundant (backup) power and cooling subsystems. RAMAC also uses multilevel caching to improve performance and it uses predictive failure analysis to identify potential disk failures.
The RAMAC subsystem can be addressed by any operating system (such as IBM's OS/390) that currently works with IBM's main storage controller products. RAMAC is scalable from nine gigabytes up to 90 gigabytes of storage.