The keyboard for IBM PC-compatible computers is standardized. However, during the more than 30 years of PC architecture being frequently updated, many keyboard layout variations have been developed.
A well-known class of IBM PC keyboards is the Model M. Introduced in 1984 and manufactured by IBM, Lexmark, Maxi Switch and Unicomp, the vast majority of Model M keyboards feature a buckling spring key design and many have fully swappable keycaps.
A numeric keypad, number pad, numpad, or ten key, is the calculator-style group of ten numeric keys accompanied by other keys, usually on the far right side of computer keyboard. This grouping allows quick number entry with the right hand, without the need to use both hands on number row of main keyboard. On a standard IBM PC keyboard, numpad has 17 keys, including digits 0 to 9, + (addition), - (subtraction), * (multiplication), and / (division) symbols, . (decimal point), Num Lock, and ⌅ Enter keys. On smaller keyboards (such as those found on laptops), the numeric keypad can be implemented as alternative markings on alphabetic keys (usually I-O-P, K-L-;, ,-.-/) or added as a separate unit, that can be connected to a device by means such as USB; some of these may include keys not found on a standard numpad, such as a spacebar or a 00 (or 000) key.
Sometimes it is necessary to distinguish between a key on the numpad and an equivalent key elsewhere on the keyboard. For example, depending on the software in use, pressing the numpad's 0 key may produce different results than pressing the alphanumeric 0 key. In such cases, the numpad-specific key may be indicated as e.g. Numpad 0, NumPad0, Num 0, or likewise to remove ambiguity.
On computer keyboards, the Esc key Esc (named Escape key in the international standard series ISO/IEC 9995) is a key used to generate the escape character (which can be represented as ASCII code 27 in decimal, Unicode U+001B, or Ctrl+[). The escape character, when sent from the keyboard to a computer, often is interpreted by software as "stop", "cancel" or "exit", and when sent from the computer to an external device (including many printers since the 1980s, computer terminals and Linux consoles, for example) marks the beginning of an escape sequence to specify operating modes or characteristics generally.
It is now generally placed at the top left corner of the keyboard, a convention dating at least to the original IBM PC keyboard, though the key itself originated decades earlier with teletypewriters.
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