1. An input/output (I/O) control system for use in a multi-partition computer system comprising: an I/O processor (IOP) partition comprising an IOP cell containing at least one CPU to execute a first control program; and a plurality of standard partitions, each including a cell comprising at least one CPU to execute a second control program, the plurality of standard partitions coupled, via shared memory, to the IOP cell; wherein at least one of the standard partitions is to become an enrolled partition in response to requesting a connection to the IOP cell; wherein, in response to a request from the enrolled partition, the IOP cell is to provide to the enrolled partition a virtualized I/O subsystem that controls I/O operations directed to a virtual I/O device including a logical entity; and wherein the enrolled partition includes a driver to: receive an I/O request; determine whether the I/O request is for the virtual I/O device or a non-virtual I/O device; process the I/O request in the enrolled partition without sending the I/O request to the IOP cell, in response to determining that the I/O request is for the non-virtual I/O device; and send the I/O request to the IOP cell, in response to determining that the I/O request is for the virtual I/O device.