Preventing initial program load failures

摘要

Means are provided to prevent the failure of an Initial Program Load (IPL) command in a data processing system because of a "busy" indication from a Direct Access Storage Device (DASD) control device which is executing the command. An IPL operation from a Central Processing Unit (CPU) involves the issuance of a System Reset signal to all channels and control units connected to the CPU, followed a short time later by a READ IPL command to the DASD control device controlling the DAS device which contains the program to be loaded. The present invention enables the system to distinguish between when a control device is busy with a System Reset procedure and when it is busy on other matters, and to permit the queueing of the READ IPL command when the control unit is busy and there is a System Reset operation pending so that the READ IPL command will not be rejected.