This is a 1024 I/O Control Module.
The Input/Output Control Module coordinates
communications between the processor and the
621 I/O system and formats the data flowing between
the I/O system and the processor. It also monitors
individual I/O module fault diagnostics. The IOCM
works in conjunction with the Parallel Link Driver
Module and/or Serial Link Module to control data
flow to I/O. The IOCM is installed in slot G in the
620-25 and slot I of the 620-35.