Parallel power supply module model no :- 621-9937 origin :- USA the parallel I/O module (PIOM) provides the link to the processor rack and to other i/o racks in a parallel i/o configuration. the PIOM decodes I/O module address data received from the PIOM and generates card selects to the appropriate I/O cards in its rack. Slot n of the I/O full rack or slot h of the I/O half rack houses the PIOM.