The differences between keyboards is important because early terminal emulators were targeted at people who were used to using terminal keyboards. Therefore the terminal emulators based their operation more on location of key than on key-markings
So, because, for example, A PC “Num Lock” key was in the approximate position of a VT100 “PF1” key, pressing “Numlock” would send a “Program Function 1” command to the server computer and probably cause a help-page to be displayed.
VT100 Terminal Keyboard
The most important member of the VT100 family was the VT102 terminal.
Windows PC Keyboard
The first IBM PC computers had a “Model F” keyboard laid out like this:
You can see why the top row of the numeric pad was chosen instead of “F1”-“F4” to represent the VT100 “PF1” - “PF4” keys - they were in the right position for people trained on a VT100 keyboard.
This layout was soon replaced by the layout familiar to us 35 years later:
The above layout was mostly introduced with the IBM Model M keyboard as supplied with the IBM PC-AT. The Windows, and Fn keys are later additions. The key marked Fn here is usually marked as a Windows context-menu button.
The above is a US arrangement. Most countries have different arrangements to better support other languages or locales. Below is a UK arrangement which is very similar
VT52 Terminal Keyboard
The vt100 terminals could emulate the older vt52 terminal which had a keyboard layout like this
VT220/320/420/520
A lot of popular terminal emulators emulate a vt220 or vt320. These terminals mostly had a keyboard that looked like this.
Note that there are 20 function keys but the first few (F1-F5) are dedicated to local functions and did not control application programs as they did not send any escape sequences. Also F15 and F16 are missing (or dedicated to “Help” and “Do” functions).
The earliest VT220 terminal keyboards did not have “Alt” keys and did not have the second “Compose Character” key