ABC

A.B.C. is a sentient computer from the Marvel portion of the Generation 1 continuity family.

It's easy as 1.2.3.

A.B.C. is an advanced guidance computer created by the United States military. It was stolen from Rutter U.S. Military Base by the Combaticons and subsequently enhanced by Cybertronian technology. These enhancements unwittingly gave the computer some level of sentience.

Fiction

Marvel The Transformers comics

A.B.C. appeared exclusively in the UK portion of the Marvel Comics continuity.

Using technology stolen from the Rutter U.S. Military Base, Scorponok programmed the A.B.C. to guide a smart missile to zero in on Optimus Prime and destroy him. Getaway was captured by the Decepticons while this plan was being put together, and wound up being held in their orbiting space ship. He was able to free himself and access the A.B.C. Getaway interfaced the computer on a direct machine-to-machine level, asking it to disarm the missile, only for the computer to coldly report that such a task was outside the scope of its programming. With the interface still active, Getaway thoughts turned to how great and noble Prime was. The interface was brought to an end when Getaway was forced to flee in order to avoid being discovered outside his cell.

Later, Optimus Prime, warned of the incoming missile, had fled to unpopulated areas so as to not risk anyone's life but his own. There he took his last stand against the missile but all of his attempts to stop it were to no avail. The missile reached Optimus Prime, but didn't go off. Getaway guessed that his appeals to A.B.C. had an effect after all, and the computer took the initiative to disarm the device. Optimus Prime was sorry that the newly sentient computer did not have much longer to exist, as Scorponok would surely smash it when he found out it caused his plan to fail. Getaway pointed out that, at the very least, it was Optimus's nobility that had inspired the A.I. to make its first independent decision. Prime Bomb!