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+The terms **ANSI** and **ISO** refer to the two main classes of [[physical_keyboard_layout|physical keyboard layouts]] western keyboard. The terms ANSI and ISO are abbreviations for **American National Standards Institute** and **International Organization for Standardization** respectively. ANSI and ISO are physical layouts; they describe the size and position of the keys regardless of the logical layout (US QWERTY, UK QWERTY, German QWERTZ, French AZERTY, Colemak, etc.). Japan has its own keyboard layout, [[ANSI_vs_JIS|JIS]], similar to ISO, but with three additional keys. The terms "ANSI" and "ISO" are also used to describe ISO keyboards that have a [[Return_key|large enter]] key that consumes the union of the space occupied by both the ISO and ANSI return keys.
+===== Layouts =====
+==== ANSI ====
+ANSI layout keyboards are mostly used in the United States and the Netherlands as well as by some programmers appreciating the better use of key space. PC keyboards using the ANSI layout as used by the [[IBM_Model_M|IBM Model M]] are typically referred to as **101-key** (pre-1995), **104-key** (with the special and context menu keys added), and **87-key** (standard TLK (tenkeyless) layout). The main cluster of keys is laid out thus:
+{{::ansi_layout_basic.png?400|}}
+The blue and purple keys illustrate the keys that differ from ISO.
+==== ISO ====
+ISO keyboards are used by many European countries, and with one extra key compared to ANSI keyboards, are correspondingly referred to as **102-key**, **105-key** and **88-key** for PCs.
+{{::iso_layout_basic.png?400|}}
+The pink and purple keys illustrate the keys that differ from ANSI. In addition to having one extra key, the ISO layout has another fundamental property: the right [[Alt_key|Alt key]] is replaced with the [[Alt_Gr_key|Alt Gr key]], which is a typographic meta key that accesses the third symbol on a keyboard. The use of accents in European languages leads to the need to enter many more symbols than in the US, with keys having increased symbol overloading. For example, in the UK, the "4" key will produce "$" with the [[Shift_key|Shift key]] held, and "€" with the Alt Gr key held.