characters in the same square form in order to preserve the grid layout of the text. These Roman characters that have been fitted to a square character cell are called fullwidth, while the normal ones are called halfwidth. In some fonts these are fitted to half-squares, like some monospaced fonts, while in others they are not. Often, fonts are available in two variants, one with the halfwidth characters monospaced, and another one with proportional halfwidth characters. The name of the typeface with proportional halfwidth characters is often prefixed with "P" for "proportional". Finally, a keyboard may have a special key to tell the OS that the last kana entered should not be converted to kanji. Sometimes this is just the Return/Enter key. Thumb-shift keyboards A thumb-shift keyboard is an alternative design, popular among professional Japanese typists. Like a standard Japanese keyboard, it has hiragana characters marked in addition to Latin letters, but the layout is completely different. Most letter keys have two kana characters associated with them, which allows all the characters to fit in three rows, like in Western layouts. In the place of the space bar key on a conventional keyboard, there are two additional modifier keys, operated with thumbs - one of them is used to enter the alternate character marked, and the other is used for voiced sounds. The semi-voiced sounds are entered using either the conventional shift key operated by the little finger, or take place of the voiced sound for characters not having a voiced variant. The kana-to-kanji conversion is done in the same way as when using any other type of keyboard. There are dedicated conversion keys on some designs, while on others the thumb shift keys double as such. Rōmaji input As an alternative to direct input of kana, a number of Japanese input method editors allow Japanese text to be entered using rōmaji, which can then be converted to kana or kanji. This method does not require the use of a Japanese keyboard with kana markings. Mobile phones Keitai input The primary system used to input Japanese on earlier generations of mobile phones is based on the numerical keypad. Each number is associated with a particular sequence of kana, such as ka, ki, ku, ke, ko for '2', and the button is pressed repeatedly to get the correct kana – each key corresponds to a column in the gojūon (5 row