Windows code page

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source:http://en.wikipedia.org/wiki/Windows_code_pages

Windows code page

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Windows code pages are sets of characters or code pages (known as character encodings in other operating systems) used in Microsoft Windows systems from the 1980s and 1990s.

[hide ]

[edit ] Overview

There are two groups of code pages used in pre-Windows NT systems, which are sometimes referred as Windows code pages : OEM and ANSI code pages. The OEM code pages are used in console windows of these systems and can be considered a holdover from DOS and the original IBM PC architecture. The ANSI code pages (sometimes simply called "Windows code pages", as the OEM code pages are more related to DOS) are extended versions of the national or international standard sets, used for non-Unicode applications using the GUI of these systems. Both OEM and ANSI code pages are extended ASCII code pages.

ANSI Windows code pages, and especially the code page 1252 , are 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).^{[ 1]}

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 control codes.

[edit ] History

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.

[edit ] List

The following Windows code pages exist:

874 — Thai
1250 — East European Latin
1251 — Cyrillic
1252 — West European Latin
1253 — Greek
1254 — Turkish
1255 — Hebrew
1256 — Arabic
1257 — Baltic
1258 — Vietnamese

[edit ] Problems of code pages

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:

The code page for a system differs between machines, so files created on one machine may become unreadable on another.
Data is often improperly tagged with the code page name or id, or not tagged at all, making determination of the correct code page to read the data difficult or impossible.
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
Code pages generally only encode a small fraction of the data available on the computer natively. Proper use of Unicode allows accurate representation of all of the data on the machine.^{[clarification needed ]}
Data expressed in an unknown code page may be converted to ???????? or worse, but can correctly round trip in Unicode.^{[clarification needed ]}