Programmable Two-Channel Switch Suspend Outboard I/O Command
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
This article describes an arrangement which provides physical configuration information by way of software without affecting system operation. The programmable two-channel switch (PTCS) feature on the IBM Series/1 processor allows devices to be connected as common to two CPUs. These common input/output (CIO) devices may be switched back and forth between the CPUs via program control. Software support for this feature must include tables identifying which devices are CIO devices, since at any time these devices may or may not be logically connected to the CPU. When a CPU first powers up, the software is required to establish which devices are CIO devices and which are not. However, while a CPU has control of the PTCS and access to the CIO devices, it is impossible to determine which devices are common.