Here you can see a 25-pin RS-232 serial port and a Centronics printer port. The port labeled "phone" is where users hooked up a special cable to interface with the internal modem. To the right of that is a cassette tape interface. You'd plug in an everyday tape recorder and record your data on the cassette. External disk drives were available for the 100, but not common.
Peeking in from the left is the reset button, which the user needs from time to time due to a few pesky bugs in the ROM code, reminding us that even non-Windows systems can crash.