requirements, for example the CTC control unit logical address of the remote CTC communicating system, when a shared channel path is used. 1.1.1 I/O sharing I/O sharing was already possible in a pre-MIF ESCON® environment, where multiple systems could share control units, devices, and common links through ESCON Directors. Channel assignment, however, was more static. Channels could only be defined as reconfigurable, were dedicated to one logical partition at a particular time, and could not be shared by other logical partitions. Multiple Image Facility (MIF) provides the same communication between logical partitions and I/O devices, but uses fewer physical channels and therefore, fewer ESCON Director ports and possible control unit link interfaces. Also, manual reassignment of channels between logical partitions to handle different workloads is no longer necessary, which improves reliability and availability. With MIF, the server channel subsystem provides channel path sharing by extending the logical addressing capability of the ESCON architecture to host images (PR/SM logical partitions). Each logical partition has its own view of a shared channel (logical channel path image) and each control unit connected to the shared channel (subsystem image). Nevertheless, it is still possible to define non-shared channels; see Figure 1-2. Pre-MIF with MIF