A central processing unit or CPU was the part of a computer in which instructions were controlled and executed.
In 2123, the SS Mariposa carried 225 Yoshimitsu Model 4077 computer CPUs as part of its cargo when it was launched for the Ficus sector. (TNG: "Up The Long Ladder")
In 2367, Reginald Barclay created a neural scan interface that communicated his thoughts directly to the USS Enterprise-D's central processing unit, transferring much of his higher brain functions and memory to the starboard computer core. (TNG: "The Nth Degree")