of English words can be spelled using only the left hand, while only a couple of hundred words can be typed using only the right hand (the three most frequent letters in the English language, ETA, are all typed with the left hand). In addition, more typing strokes are done with the left hand in the QWERTY layout. This is helpful for left-handed people but disadvantageous for right-handed people. Contrary to popular belief, the QWERTY layout was not designed to slow the typist down, but rather to speed up typing. Indeed, there is evidence that, aside from the issue of jamming, placing often-used keys farther apart increases typing speed, because it encourages alternation between the hands. (On the other hand, in the German keyboard the Z has been moved between the T and the U to help type the frequent digraphs TZ and ZU in that language.) Almost every word in the English language contains at least one vowel letter, but on the QWERTY keyboard only the vowel letter "A" is on the home row, which requires the typist's fingers to leave the home row for most words. A feature much less commented-on than the order of the keys is that the keys do not form a rectangular grid, but rather each column slants diagonally. This is because of the mechanical linkages – each key is attached to a lever, and hence the offset prevents the levers from running into each other – and has been retained in most electronic keyboards. Some keyboards, such as the Kinesis or TypeMatrix, retain the QWERTY layout but arrange the keys in vertical columns, to reduce unnecessary lateral finger motion. Computer keyboards The first computer terminals such as the Teletype were typewriters that could produce and be controlled by various computer codes. These used the QWERTY layouts and added keys such as escape (ESC) which had special meanings to computers. Later keyboards added function keys and arrow keys. Since the standardization of PC-compatible computers and Windows after the 1980s, most full-sized computer keyboards have followed this standard (see drawing at right). This layout has a separate numeric keypad for data entry at the right, 12 function keys across the top, and a cursor section to the right and center with keys for Insert, Delete, Home, End, Page Up, and Page Down with cursor arrows in an inverted-T shape. Diacritical marks QWERTY was designed for