the initial build of the powermaster had 3 primary processors - one for each “spellcasting” class, mage cleric and psion. i think it was the 3rd or 4th gen where a “physical” processor was added - for melee, movement or whatnot. a few generations after that, a set of 4 co-processors was added, taking the load off the main brains for minor actions like ongoing spell concentration, shifting targets, gem actions, refreshing stoneskins, etc. the co-processors are limited to self/personal effects only - fiddling and diddling with things running in the background on the powermaster himself.
so, for example, if Daren was casting a prismatic spray at some lich that pissed him off, triggering the lich’s dim-door contingency - a coprocessor could re-target the ongoing spell and hit the bastard anyway (provided he was in range, obviously), but the coprocessor isn’t “smart” enough to initiate the casting in the first place as it involves both casting and targeting (a non-personal effect).