It should be noted that the first Mac 128k's were not called "Mac 128k's." As there were no other Macs to confuse it with, the computer was simply referred to as "Macintosh." The one shown here is an original, differing from the later version only in the nameplate. The original Macintosh was severely underpowered, but nonetheless revolutionary. The Lisa had already introduced the graphical user interface, but with a $9,995 price tag. The Macintosh is the computer that made this revolutionary new means of computing a possibility for everybody.
The serial number is on the bottom, beside the brightness knob: