I/O controller for controlling the sequencing of execution of I/O commands and for permitting modification of I/O controller operation by a host processor

A system for controlling input/output operations required by a host computer, which includes host processor means and host memory means, in communication with one or more input/output devices, said system comprising:

• an input/output controller unit connected to said host computer and to said one or more input/output devices for controlling said input/output operation in response to input/output commands from said host processor means, said controller unit including controller processor means and controller memory means;
• said host memory means being accessible to said controller unit for storing a plurality of control block lists, each control block list corresponding to one of said input/output commands and including control blocks of command information;
• means for transferring input/output commands from said host processor means to said controller processor means of said controller unit;
• said controller processor means being responsive to said input/output commands transferred thereto for successively accessing from said host memory the control block lists corresponding to said input/output commands;
• said controller memory means being connected to said controller processor means for storing said control block lists, each including command information, control information supplied by said host processor means, status return informatin supplied by said controller processor means, and error information concerning errors which arise during execution of the operation corresponding to said control block;
• said controller processor means includes
• means for selecting one of a plurality of different sequences of said control blocks of command information from said control block lists in accordance with a predetermined algorithm in said controller memory means;
• and
• means responsive to said selected sequence of control blocks of command information for executing the operations required by said input/output commands;
• said controller unit further including means for storing controller information concerning the operation of said controller unit and for transferring said controller information to said host processor means;
• and
• said host processor means being responsive to said controller information for selectively modifying said controller information so as to modify the operation of said controller unit and for transferring said modified controller information to said controller unit.