Understanding the Keyboards

If an application is reading input directly from the keyboard, it receives a keycode when a key is pressed. Equivalent keys on the two keyboards are those that generate the same keycode. If an equivalent key does not exist, there is no way to generate the corresponding keycode.

In an X Window System environment, keycodes are mapped into key symbols by the X library. The key symbols are stored in a keysym table. Application programs then reference these key symbols when accessing keys.

Figure A-1 Keycap, Keycode, and Keysym Relationships

Equivalent keys are those keys that are mapped to the same key symbol. One advantage of this mapping is that if a key does not physically exist on a keyboard, its equivalent key symbol can be mapped to some other key through the corresponding keycode.