History of IBM CKD Controllers (original) (raw)

Beginning with its 1964 System/360 announcement, IBM's mainframes initially accessed CKD (Count key data) subsystems via a channel connected to separate Storage Control Units (SCUs) with attached Direct Access Storage Devices (DASD), typically a hard disk drive. This practice continued in IBM's larger mainframes thru System/370; however low end systems generally used lower cost integrated attachments where the function of the SCU was combined with that of the channel, typically called an Integrated File Adapter.