RedGrittyBrick

PC and VT100 Keyboard Layouts Compared

This covers

Windows PC Keyboard

Most full-size PC keyboards have one of three physical layouts: ANSI, ISO or JIS.

ANSI

The physical layout most popular in the US is named the ANSI layout. A few other countires use this physical layout, but often with some letters and other characters in different positions.

Diagram of Typical Windows/PC keyboard layout

The above layout was mostly introduced with the IBM Model M keyboard as supplied with the IBM PC-AT (see history further below).
The Windows, and Fn keys are later additions. The key marked Fn here is usually marked as a Windows context-menu button.

ISO

Most countries have different arrangements to better support other languages or locales. I believe most are based on the ISO layout. Below is a UK ISO keyboard.

Diagram of UK PC 105-key keyboard layout

JIS

The Japanese layout has the larger left-shift of ANSI and the vertical Return-key of ISO but with a lot of extra keys created partly by having smaller space-bar and backspace keys.

Diagram of an invented JIS keyboard

Note the above is a hybrid of several different JIS keyboards, they seem to vary a lot. The Japanese inscriptions are omitted until I find time to work around restrictions in my image production process.

Compact Keyboards

Nowadays smaller keyboards have become a little more popular, especially among the “mechanical” keyboard community - people who prefer the feel of more complex switches than those found in low-cost keyboards based on rubber membrane switches.

Diagram of Vortex Race 3

Diagram of Drevo Calibur 2

Diagram of Tada 68

Diagram of Ducky One Mini

Diagram of Planck

Diagram of Gherkin

History

The first IBM PC computers had a “Model-F” keyboard laid out like this:

Diagram of 1981 IBM PC, XT Model-F keyboard

The later IBM PC-AT computers had a “Model-F AT” keyboard laid out like this:

Diagram of 1984 IBM Model-F AT keyboard layout

You can see why the top row of the numeric pad was chosen instead of “F1”-“F4” to represent the VT100 “PF1” - “PF4” keys in a terminal emulator program - they were in the right position for people trained on a VT100 keyboard - see below.

Ancient History

The differences between current and old 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

A very popular terminal was the VT102 terminal from the VT100 series made by Digital Equipment Corporation (DEC). When PCs first appeared terminal emulator software often emulated the VT102

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.

The key mapping was by key position not by key-label! This is not the case with modern terminal emulators though.

Teletype

Diagram of 1963 Teletype 33 keyboard

VT52 Terminal Keyboard

The VT52 terminal had a keyboard layout like this

Diagram of 1974 VT52 keyboard layout

VT102 Terminal Keyboard

A VT102 terminal could also emulate a VT52 but its keyboard looked like this

Diagram of >1978 DEC VT102 terminal keyboard layout

VT220/320/420/520

The VT100 series was superceded by VT200, VT300, VT400 and VT500 series terminals and associated keyboards like the LK411.

Diagram of ~1993 DEC LK411 keyboard layout

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 shown above.