Positronic subprocessor

From Memory Alpha, the free Star Trek reference

The positronic subprocessor is an integral piece of the positronic brain of Soong-type androids. The subprocessor is linked to information processing of subroutines within the positronic framework. It may be susceptible to energy surges that disrupt programming and cause different file directories to inaccurately exchange information. One such power surge in 2369 caused Data to accidentally absorb information from the USS Enterprise-D's main computer, specifically files related to recreational programming and the Ancient West. As a result, Data took on peculiar characteristics of holodeck characters from that setting. (TNG: "A Fistful of Datas")