Editing Code page (section)

== {{anchor|Private use|User-definable}}Private code pages ==
When, early in the history of personal computers, users did not find their character encoding requirements met, private or local code pages were created using [[terminate-and-stay-resident]] utilities or by re-programming [[BIOS]] [[EPROM]]s. In some cases, unofficial code page numbers were invented (e.g. CP895).

When more diverse character set support became available most of those code pages fell into disuse, with some exceptions such as the [[Kamenický encoding|Kamenický]] or KEYBCS2 encoding for the [[Czech alphabet|Czech]] and [[Slovak alphabet|Slovak]] alphabets. Another character set is [[Iran System encoding standard]] that was created by Iran System corporation for [[Persian language]] support. This standard was in use in Iran in DOS-based programs and after introduction of Microsoft code page 1256 this standard became obsolete. However some Windows and DOS programs using this encoding are still in use and some Windows fonts with this encoding exist.

In order to overcome such problems, the [[IBM Character Data Representation Architecture]] level 2 specifically reserves ranges of code page IDs for user-definable and private-use assignments. Whenever such code page IDs are used, the user must not assume that the same functionality and appearance can be reproduced in another system configuration or on another device or system unless the user takes care of this specifically.
The code page range 57344-61439 ({{Mono|E000h}}-{{Mono|EFFFh}}) is officially reserved for user-definable code pages (or actually CCSIDs in the context of [[IBM CDRA]]), whereas the range 65280-65533 ({{Mono|FF00h}}-{{Mono|FFFDh}}) is reserved for any user-definable "private use" assignments.
For example, a non-registered custom variant of code page 437 ({{Mono|1B5h}}) or 28591 ({{Mono|6FAF}}) could become 57781 ({{Mono|E1B5h}}) or 61359 ({{Mono|EFAFh}}), respectively, in order to avoid potential conflicts with other assignments and maintain the sometimes existing internal numerical logic in the assignments of the original code pages. An unregistered private code page not based on an existing code page, a device specific code page like a printer font, which just needs a logical handle to become addressable for the system, a frequently changing download font, or a code page number with a symbolic meaning in the local environment could have an assignment in the private range like 65280 ({{Mono|FF00h}}).

The code page IDs 0, 65534 ({{Mono|FFFEh}}) and 65535 ({{Mono|FFFFh}}) are reserved for internal use by operating systems such as DOS and must not be assigned to any specific code pages.