The Macintosh 512K
In Figures 5 and 7 you have an overall look at the Macintosh 512K. Similarly to the Macintosh 128K, the Macintosh 512K had a brightness adjustment button on its front panel, below the Apple logo.
The easiest way to detect that this is the Macintosh 512K is that it has “Macintosh 512K” written on its back. The original Macintosh had only “Macintosh” or “Macintosh 128K” (models manufactured after September 1984) written on its back, and the successor to the 512K, the Macintosh Plus, had “Macintosh Plus” written on the front panel.
Another way to differentiate the original Macintosh from the Macintosh 512K is by the model number. The original Macintosh’s model number is “M0001,” while the 512K’s model number can be “M0001W” (for the original model with a 400 kB floppy disk drive), “M0001E” (for the 512Ke model, with an 800 kB floppy disk drive) or “M0001D” (for the 512Ke/800 model, with an 800 kB floppy disk drive and the same keyboard as the Macintosh Plus).
On the rear panel, the computer had a compartment for you to install a 4.5 V battery (known as TR133R, NEDA 1306A, 523, etc.) in charge of keeping the computer’s real time clock hardware working when the computer was turned off. Notice that this battery has the same physical size of a AA battery, but it is different (4.5 V vs. 1.5 V).
At the bottom part of the rear panel, the Macintosh 512K had a proprietary mouse port, a port for the installation of an external floppy disk drive, a serial port for a printer, a serial port for an external modem, and a 3.5 mm jack for an external speaker. The Macintosh 512K had an internal speaker as well. This configuration is exactly the same as the Macintosh 128K.
It is interesting to note that while the serial port used on the PC used a male connector, the serial port used on the Macintosh used a female connector.