M-4 multitronic unit
From Memory Alpha, the free Star Trek reference
The M-4 multitronic unit was also a failed computer version of the M-5 multitronic unit and was deemed by Richard Daystrom as "not entirely successful". The M-4 was the fourth in a series of multitronic computers (beginning with the M-1) which were designed to run a starship with a minimal crew of just under thirty personnel. The failure of the M-4 led to the design and development of the M-5. (TOS: "The Ultimate Computer")
