The local disk controller

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Abstract
The performance of the I/O subsystem in the 370-XA architecture has been improved considerably with the introduction of the new channel subsystem, as compared to the System/370 architecture. The emphasis in the 370-XA architecture is on reducing the CPU load associated with I/O, and on reducing the congestion in multi-CPU, shared systems, by redesigning the channel system.In this paper we will show that a reallocation of the control unit logic may triple the channel subsystem's capacity, while still using the same disk drives. The performance gain is achieved by adding control-unit like intelligence and local buffer memory to each disk drive, creating a Local Disk Controller (LDC), and thus eliminating the performance degradation caused by reconnect failures at a high channel utilization. The system proposed remains fully software compatible with the current 370-XA architecture. A simpler approach, requiring only a slight modification to the disk drives, is also discussed.

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