Home of the original IBM PC emulator for browsers.
This is a test of two VT100 Terminals whose serial ports are virtually connected, so anything you type in the first terminal should appear on the screen of the second, and vice versa. Click or tap on the screen of the desired terminal before you begin typing. A Dual Diagnostic Configuration is also available.
If either terminal becomes LOCKED, press the SET-UP key (mapped to your F9 function key) twice to unlock it.