Windows code page

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 is a misnomer because the behavior does not exactly match ANSI and because many non-ANSI standard encodings are allowed in these 8-bit code pages, most recently UTF-8 Unicode.

Most legacy "ANSI" code pages have code page numbers in the pattern 125x. However, 874 (Thai) and the East Asian multi-byte "ANSI" code pages (932, 936, 949, 950), all of which are also used as OEM code pages, are numbered to match similar (but not identical) IBM encodings. While code page 1258 is also used as an OEM code page, it is original to Microsoft rather than an extension to an existing encoding. IBM have assigned their own, different numbers for Microsoft's variants, these are given for reference in the lists below where applicable.

All of the 125x Windows code pages, as well as 874 and 936, are labelled by Internet Assigned Numbers Authority (IANA) as "Windows-number", although "Windows-936" is treated as a synonym for "GBK". Windows code page 932 is instead labelled as "Windows-31J".[3]

ANSI Windows code pages, and especially the code page 1252, were so-called 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:[2]

• 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)
• Having no parallel encoding (like Windows-1257 vs. ISO-8859-4; ISO-8859-13 was introduced much later). Also, Windows-1251 follows neither the ISO-standardised ISO-8859-5 nor the then-prevailing KOI-8.

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.

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 descendant) 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.[4] 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 was introduced after many of the ANSI and OEM code pages were introduced; several code pages were revised to contain the euro sign.

Since version 1803, Windows machines can be configured to allow UTF-8 as the "ANSI" and OEM codepage.[5]

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.

• Programs need to know what code page to use in order to display the contents of files correctly. If a program uses the wrong code page it may show text as mojibake.
• The code page in use may differ between machines, so files created on one machine may be unreadable on another.
• Data is often improperly tagged with the code page, or not tagged at all, making determination of the correct code page to read the data difficult.
• These Microsoft code pages differ to various degrees from some of the standards and other vendors' implementations. This isn't a Microsoft issue per se, as it happens to all vendors, but the lack of consistency makes interoperability with other systems unreliable in some cases.
• The use of code pages limits the set of characters that may be used.
• Characters expressed in an unsupported code page may be converted to question marks (?) or other replacement characters, or to a simpler version (such as removing accents from a letter). In either case, the original character may be lost.

• AppLocale – a utility to run non-Unicode (code page-based) applications in a locale of the user's choice.

• National Language Support (NLS) API Reference. Table showing ANSI and OEM codepages per language (from web-archive since Microsoft removed the original page)
• IANA Charset Name Registrations
• Unicode mapping table for Windows code pages
• Unicode mappings of windows code pages with "best fit"