The combat computor was a component of the Dalek casing by the time the Grey Daleks were in wide use by the Dalek Empire. It was a slab of hardware contained in the dome section, thus resting directly above the photo-sonic cells, themselves above the environment chamber housing the Dalek creature.
The combat computor section of the casing marked as "C" on a Space Intelligence Service diagram of Dalek anatomy. (PROSE: Inside a Dalek)
The combat computor was an advanced memory cell which contained every war strategy known to the Daleks. Thanks to it, the Dalek pilot could react within microseconds to any combat situation. (PROSE: Inside a Dalek)