Characters that did not exist in that page (such as a line-drawing graphic from the OEM page when the software was using the Windows code page) could not be inserted, and either were ignored or produced an unexpected character. īefore Unicode was introduced, most Windows software could only create text using the repertoire of characters available in a single code page.
Typing these numbers with a leading zero is ignored. The numbers 0 –31 and 127 are control characters in the Windows code pages. But prefixing a leading zero (0) to the number (usually meaning 4 digits) produced the character specified by the newer Windows code page, allowing them to be typed as well.įor instance, the combination Alt+ 1 6 3 would result in ú (Latin letter u with acute accent) which is at 163 in the OEM code page of CP437 or CP850, while Alt+ 0 1 6 3 yields the character £ (symbol for the pound sterling) which is at 163 in CP1252. The old code pages were called OEM code pages the new ones are called Windows code pages, The familiar Alt+number combinations produced codes from the OEM code page (for example, CP437 in the United States), matching the results from MS-DOS. The Alt codes had become so well known and memorized by users that Microsoft decided to preserve them, even though it used a new and different set of code pages for Windows, such as CP1252.
#ALT KEY ON MAC WHAT ON WINDOWS PC#
PC keyboards designed for non-English use included other methods of inserting these characters, such as national keyboard layouts, the AltGr key or dead keys, but the Alt key was the only method of inserting some characters and the only method that was the same on all machines, so it remained very popular. (There were, however, many more code pages for a more complete list, see code page). A common choice in locales using variants of the Latin alphabet was CP850, which provided more Latin character variants. This causes the Alt combinations to produce different characters (as well as changing the display of any previously-entered text in the same manner).
Some Eastern European, Arabic and Asian computers used other hardware code pages, and MS-DOS was able to switch between them at runtime with commands like KEYB, CHCP or MODE.
In most cases typing a number greater than 255 produced the character associated with the remainder after the number is divided by 256. Some would interpret the code as a command, but often it would be interpreted as a code to be placed on the screen at the location of the cursor, thus displaying the corresponding 8-bit character from the current code page. Applications reading keystrokes from the BIOS would behave according to what action they associate with that code. It would place the corresponding code into the keyboard buffer so that it would look (almost) as if the code had been entered by a single keystroke. On IBM PC compatible personal computers from the 1980s, the BIOS allowed the user to hold down the Alt key and type a decimal number on the keypad.
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