The Keyboard configuration panel allows you to control the behaviour of the keyboard in PuTTY.
Some terminals believe that the Backspace key should send the same thing to the server as Control-H (ASCII code 8). Other terminals believe that the Backspace key should send ASCII code 127 (usually known as Control-?) so that it can be distinguished from Control-H. This option allows you to choose which code PuTTY generates when you press Backspace.
If you are connecting to a Unix system, you will probably find that the Unix stty command lets you configure which the server expects to see, so you might not need to change which one PuTTY generates. On other systems, the server's expectation might be fixed and you might have no choice but to configure PuTTY.
If you do have the choice, we recommend configuring PuTTY to generate Control-? and configuring the server to expect it, because that allows applications such as emacs to use Control-H for help.
The Unix terminal emulator rxvt disagrees with the rest of the world about what character sequences should be sent to the server by the Home and End keys.
xterm, and other terminals, send ESC [1~ for the Home key, and ESC [4~ for the End key. rxvt sends ESC [H for the Home key and ESC [Ow for the End key.
If you find an application on which the Home and End keys aren't working, you could try switching this option to see if it helps.
This option affects the function keys (F1 to F12) and the top row of the numeric keypad.
ESC [n~, the function keys generate sequences like ESC [11~, ESC [12~ and so on. This matches the general behaviour of Digital's terminals.ESC [[A through to ESC [[E. This mimics the Linux virtual console.ESC OP through to ESC OS, which are the sequences produced by the top row of the keypad on Digital's terminals.ESC OP through to ESC OS.ESC OP through to ESC O[ESC [M through to ESC [X. Together with shift, they generate ESC [Y through to ESC [j. With control they generate ESC [k through to ESC [v, and with shift and control together they generate ESC [w through to ESC [{.If you don't know what any of this means, you probably don't need to fiddle with it.
Application Cursor Keys mode is a way for the server to change the control sequences sent by the arrow keys. In normal mode, the arrow keys send ESC [A through to ESC [D. In application mode, they send ESC OA through to ESC OD.
Application Cursor Keys mode can be turned on and off by the server, depending on the application. PuTTY allows you to configure the initial state, and also allows you to disable application mode completely.
Application Keypad mode is a way for the server to change the behaviour of the numeric keypad.
In normal mode, the keypad behaves like a normal Windows keypad: with NumLock on, the number keys generate numbers, and with NumLock off they act like the arrow keys and Home, End etc.
In application mode, all the keypad keys send special control sequences, including Num Lock. Num Lock stops behaving like Num Lock and becomes another function key.
Depending on which version of Windows you run, you may find the Num Lock light still flashes on and off every time you press Num Lock, even when application mode is active and Num Lock is acting like a function key. This is unavoidable.
Application keypad mode can be turned on and off by the server, depending on the application. PuTTY allows you to configure the initial state, and also allows you to disable application mode completely.
PuTTY has a special mode for playing NetHack. You can enable it by selecting "NetHack" in the "Initial state of numeric keypad" control.
In this mode, the numeric keypad keys 1-9 generate the NetHack movement commands (hjklyubn). The 5 key generates the . command (do nothing).
Better still, pressing Shift with the keypad keys generates the capital forms of the commands (HJKLYUBN), which tells NetHack to keep moving you in the same direction until you encounter something interesting.
For some reason, this feature only works properly when Num Lock is on. We don't know why.
DEC terminals have a Compose key, which provides an easy-to-remember way of typing accented characters. You press Compose and then type two more characters. The two characters are "combined" to produce an accented character. The choices of character are designed to be easy to remember; for example, composing "e" and "`" produces the "è" character.
If you enable the "Application and AltGr act as Compose key" option, the Windows Application key and the AltGr key will both have this behaviour.
Some old keyboards do not have an AltGr key, which can make it difficult to type some characters. PuTTY can be configured to treat the key combination Ctrl + Left Alt the same way as the AltGr key.
By default, this checkbox is checked, and the key combination Ctrl + Left Alt does something completely different. PuTTY's usual handling of the left Alt key is to prefix the Escape (Control-[) character to whatever character sequence the rest of the keypress would generate. For example, Alt-A generates Escape followed by a. So Alt-Ctrl-A would generate Escape, followed by Control-A.
If you uncheck this box, Ctrl-Alt will become a synonym for AltGr, so you can use it to type extra graphic characters if your keyboard has any.