One implementation of the GKOS keyboard
The GKOS keyboard standard for small portable terminals is intended for replacing the QWERTY where there is not enough room for a large number of keys but still all QWERTY functions are required. Typical applications are cellular terminals/browsers and tablet PCs.
The GKOS keyboard has 6 keys and they are located on the back of the terminal, 3 keys for each hand. The keypad is split between two hands so that the combination of keys to press would not be too difficult physically, and in order to have the keys where the fingers are when you hold a calendar shaped object vertically in front of you by two hands.
For letters, numbers and punctuation, the most difficult combination is pressing two keys simultaneously by one hand while the other hand presses one key or no key at all. The remaining combinations are used for other functions found on the QWERTY keyboard. The thumbs can be used to control the mouse functions on the front panel near the sides. Consequently, most of the front panel can be reserved for the display (wide screen shape). The GKOS keyboard is also referred to as the "SixBack".
See also: chorded keyboard