Re: Ipa Keyboard Layouts For Mac
Kasey Finkenbinder
A keyboard layout is any specific physical, visual, or functional arrangement of the keys, legends, or key-meaning associations (respectively) of a computer keyboard, mobile phone, or other computer-controlled typographic keyboard.
Physical layout is the actual positioning of keys on a keyboard. Visual layout is the arrangement of the legends (labels, markings, engravings) that appear on those keys. Functional layout is the arrangement of the key-meaning association or keyboard mapping, determined in software, of all the keys of a keyboard; it is this (rather than the legends) that determines the actual response to a key press.
The core section of a keyboard consists of character keys, which can be used to type letters and other characters. Typically, there are three rows of keys for typing letters and punctuation, an upper row for typing digits and special symbols, and the Space bar on the bottom row. The positioning of the character keys is similar to the keyboard of a typewriter.
Typically, a modifier key is held down while another key is struck. To facilitate this, modifier keys usually come in pairs, one functionally identical key for each hand, so holding a modifier key with one hand leaves the other hand free to strike another key.
Compared with the secondary-shift modifier key, the dead-key approach may be a little more complicated, but it allows more additional letters. Using AltGr, only one or (if used simultaneously with the normal shift key) two additional letters with each key, whereas using a dead key, a specific diacritic can be attached to a range of different base letters.
A Compose key can be characterized as a generic dead key that may in some systems be available instead of or in addition to the more specific dead keys. It allows access to a wide range of predefined extra characters by interpreting a whole sequence of keystrokes following it. For example, striking Compose followed by ' (apostrophe) and then A results in (a with acute accent), Compose followed by A and then E results in (ae ligature), and Compose followed by O and then C results in (circled c, copyright symbol).
Depending on the application, some keyboard keys are not used to enter a printable character but instead are interpreted by the system as a formatting, mode shift, or special commands to the system. The following examples are found on personal computer keyboards.
The system request (SysRq) and print screen (PrtSc or on some keyboards e.g. PrtScn) commands often share the same key. SysRq was used in earlier computers as a "panic" button to recover from crashes (and it is still used in this sense to some extent by the Linux kernel; see Magic SysRq key). The print screen command is used to capture the entire screen and send it to the printer, but in the present, it usually puts a screenshot in the clipboard.
The Break key/Pause key no longer has a well-defined purpose. Its origins go back to teleprinter users, who wanted a key that would temporarily interrupt the communications line. The Break key can be used by software in several different ways, such as to switch between multiple login sessions, to terminate a program, or to interrupt a modem connection.
In programming, especially old DOS-style BASIC, Pascal and C, Break is used (in conjunction with Ctrl) to stop program execution. In addition to this, Linux and variants, as well as many DOS programs, treat this combination the same as Ctrl+C. On modern keyboards, the break key is usually labeled Pause/Break. In most Microsoft Windows environments, the key combination WindowsPause brings up the system properties.
Historically it also served as a type of shift key, such that one or more following characters were interpreted differently, hence the term escape sequence, which refers to a series of characters, usually preceded by the escape character.[11][12]
On machines running Microsoft Windows, prior to the implementation of the Windows key on keyboards, the typical practice for invoking the "start" button was to hold down the control key and press escape. This process still works in Windows 10 and 11.[13]
An "enter" key may terminate a paragraph of text and advance an editing cursor to the start of the next available line, similar to the "carriage return" key of a typewriter. When the attached system is processing a user command line, pressing "enter" may signal that the command has been completely entered and that the system may now process it.
Shift key: when one presses shift and a letter, it will capitalize the letter pressed with the shift key. Another use is to type more symbols than appear to be available, for instance the semi-colon key is accompanied with a colon symbol on the top. To type a semi-colon, the key is pressed without pressing any other key. To type a colon, both this key and the Shift key are pressed concurrently. (Some systems make provision for users with mobility impairment by allowing the Shift key to be pressed first and then the desired symbol key).
Keyboard layouts have evolved over time, usually alongside major technology changes. Particularly influential have been: the Sholes and Glidden typewriter (1874, also known as Remington No. 1), the first commercially successful typewriter, which introduced QWERTY;[14] its successor, the Remington No. 2 (1878), which introduced the shift key; the IBM Selectric (1961), a very influential electric typewriter, which was imitated by computer keyboards;[15] and the IBM PC (1981), namely the Model M (1985), which is the basis for many modern keyboard layouts.
The earliest mechanical keyboards were used in musical instruments to play particular notes. With the advent of the printing telegraph, a keyboard was needed to select characters. Some of the earliest printing telegraph machines either used a piano keyboard outright or a layout similar to a piano keyboard.[16][17] The Hughes-Phelps printing telegraph piano keyboard laid keys A-N in left-to-right order on the black piano keys, and keys O-Z in right-to-left order on the white piano keys below.
In countries using the Latin script, the center, alphanumeric portion of the modern keyboard is most often based on the QWERTY design by Christopher Sholes. Sholes' layout was long thought to have been laid out in such a way that common two-letter combinations were placed on opposite sides of the keyboard so that his mechanical keyboard would not jam. However, evidence for this claim has often been contested. In 2012, an argument was advanced by two Japanese historians of technology showing that the key order on the earliest Sholes prototypes in fact followed the left-right and right-left arrangement of the contemporary Hughes-Phelps printing telegraph, described above.[18] Later iterations diverged progressively for various technical reasons, and strong vestiges of the left-right A-N, right-left O-Z arrangement can still be seen in the modern QWERTY layout. Sholes' chief improvement was thus to lay out the keys in rows offset horizontally from each other by three-eighths, three-sixteenths, and three-eighths inches to provide room for the levers and to reduce hand-movement distance. Although it has been demonstrated that the QWERTY layout is not the most efficient layout for typing,[19] it remains the standard.
On a manual typewriter, the operator could press the key down with a lighter touch for such characters as the period or comma, which did not occupy as much area on the paper. Since an electric typewriter supplied the force to the typebar itself after the typist merely touched the key, the typewriter itself had to be designed to supply different forces for different characters. To simplify this, the most common layout for electric typewriters in the United States differed from that for the one most common on manual typewriters. Single-quote and double-quote, instead of being above the keys for the digits 2 and 8 respectively, were placed together on a key of their own. The underscore, another light character, replaced the asterisk above the hyphen.
The ASCII communications code was designed so that characters on a mechanical teletypewriter keyboard could be laid out in a manner somewhat resembling that of a manual typewriter. This was imperfect, as some shifted special characters were moved one key to the left, as the number zero, although on the right, was low in code sequence. Later, when computer terminals were designed from less expensive electronic components, it was not necessary to have any bits in common between the shifted and unshifted characters on a given key. This eventually led to standards being adopted for the "bit-pairing" and "typewriter-pairing" forms of keyboards for computer terminals.
The typewriter-pairing standard came under reconsideration, on the basis that typewriters have many different keyboard arrangements.[20] The U.S. keyboard for the IBM PC, although it resembles the typewriter-pairing standard in most respects, differs in one significant respect: the braces are on the same two keys as the brackets, as their shifts. This innovation predated the IBM Personal Computer by several years.[21]
Most modern keyboards basically conform to the layout specifications contained in parts 1, 2, and 5 of the international standard series ISO/IEC 9995. These specifications were first defined by the user group at AFNOR in 1984 working under the direction of Alain Souloumiac.[22] Based on this work, a well-known ergonomic expert wrote a report[23] which was adopted at the ISO Berlin meeting in 1985 and became the reference for keyboard layouts.
Physical layouts only address tangible differences among keyboards. When a key is pressed, the keyboard does not send a message such as the A-key is depressed but rather the left-most main key of the home row is depressed. (Technically, each key has an internal reference number, the scan code, and these numbers are what is sent to the computer when a key is pressed or released.) The keyboard and the computer each have no information about what is marked on that key, and it could equally well be the letter A or the digit 9. Historically, the user of the computer was requested to identify the functional layout of the keyboard when installing or customizing the operating system. Modern USB keyboards are plug-and-play; they communicate their visual layout to the OS when connected (though the user is still able to reset this at will).[example needed]
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