Windows code pages are sets of characters or code pages (known as character encodings in other operating systems) used in Microsoft Windows from the 1980s and 1990s. Windows code pages were gradually superseded when Unicode was implemented in Windows, although they are still supported both within Windows and other platforms.
There are two groups of code pages used in pre-Windows NT systems: OEM and ANSI code pages. Code pages in both of these groups are extended ASCII code pages.
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ANSI code pages (officially called "Windows code pages"[1] after Microsoft accepted the former term being a misnomer[2]) are used for native non-Unicode (say, byte oriented) applications using a graphical user interface on Windows systems. ANSI Windows code pages, and especially the code page 1252, were called that way since they were purportedly based on drafts submitted or intended for ANSI. However, ANSI and ISO have not standardized any of these code pages. Instead they are either supersets of the standard sets such as those of ISO 8859 and the various national standards (like Windows-1252 vs. ISO-8859-1), major modifications of these (making them incompatible to various degrees, like Windows-1250 vs. ISO-8859-2) or having no parallel encoding (like Windows-1257 vs. ISO-8859-4; ISO-8859-13 was introduced much later).[2] About twelve of the typography and business characters from CP1252 at code points 0x80–0x9F (in ISO 8859 occupied by C1 control codes, which are useless in Windows) are present in many other ANSI/Windows code pages at the same codes. These code pages are labelled by Internet Assigned Numbers Authority (IANA) as "Windows-number".[3]
The OEM code pages (original equipment manufacturer) are used by Win32 console applications, and by virtual DOS, and can be considered a holdover from DOS and the original IBM PC architecture. A separate suite of code pages was implemented not only due to compatibility, but also because the fonts of VGA (and descendent) hardware suggest encoding of line drawing characters to be compatible with code page 437. Most OEM code pages share many code points, particularly for non-letter characters, with the second (non-ASCII) half of CP437.
A typical OEM code page, in its second half, does not resemble any ANSI/Windows code page even roughly. Nevertheless, two single-byte, fixed-width code pages (874 for Thai and 1258 for Vietnamese) and four multibyte CJK code pages (932, 936, 949, 950) are used as both OEM and ANSI code pages. Code page 1258 uses combining diacritics, as Vietnamese requires more than 128 letter-diacritic combinations. This is in contrast to VISCII, which replaces some of the C0 (i.e. ASCII) control codes.
Initially, computer systems and system programming languages did not make a distinction between characters and bytes. This led to much confusion subsequently. Microsoft software and systems previous to the Windows NT line are examples of this, using the OEM and ANSI code pages, which do not make the distinction.
Since the late 1990s, software and systems are increasingly adopting more direct encodings of Unicode, in particular UTF-8 and UTF-16; this trend has been improved by the widespread adoption of XML, which provides a more adequate mechanism for labelling the encoding used. Recent Microsoft products and application program interfaces use Unicode internally, but many applications and APIs continue to use the default encoding of the computer's locale when reading and writing text data to files or standard output. Therefore, though Unicode is the accepted standard, there is still backwards compatibility with the older Windows code pages.
The euro sign is a recent addition to ANSI code pages, and certain fonts may not display it.
The following Windows code pages exist:
Microsoft strongly recommends using Unicode in modern applications, but many applications or data files still depend on the legacy code pages. This can cause many problems:
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