System for dynamic association of a variable number of device addresses with input/output devices to allow increased concurrent requests for access to the input/output devices

摘要

Disclosed is a data processing system for presenting concurrent requests for access to peripheral devices up to the number of subchannels available for handling input/output operations. A computer system provides a plurality of subchannels and affiliated unit control blocks for input/output operations between main storage and the peripheral devices. The unit control blocks comprise two groups, including a first dedicated to the peripheral devices and a second group available for dynamic association with the peripheral devices on a demand basis. The unit control blocks are termed base unit control blocks and alias unit control blocks, respectively. Upon system initialization, alias unit control blocks for a given logical subsystem are linked in a free pool. To initiate an input/output operation a program executing on the CPU first queries a base unit control block for a target peripheral device to determine its availability. If available, the base unit control block and associated base subchannel are used for the input/output operation. If not, determination is made if an alias unit control block may be used and if any are available. Responsive to affirmative determinations, an alias unit control block is removed from the free pool and is linked to the base unit control device for the target peripheral device in an exposure chain. The CPU then places a channel program in main storage including a prefix channel command for binding an alias address for the alias unit control block with a particular device. This is done by passing the binding command to a controller for the target peripheral device which maintains tables of affiliations between aliases and peripheral devices on a path group basis. After binding, the input/output operation proceeds in conventional fashion.