A common base codepage standard for Chinese is GB 2312-1980. It encodes more than 6,000 frequently-used Chinese ideographs.
With the growing importance of Unicode and the parallel standard ISO 10646 (which was adopted by China as GB 13000), an extension of GB 2312-1980 was created. This extension was called GBK and encoded all 20,902 unified ideographs that are assigned in Unicode 2.1. GBK is not a formal standard, but a widely-implemented specification.
Unicode 3.0 added more than 6,000 ideographs, and the upcoming version 3.1 will add about 42,000 on top of that.
GB 18030 was created as an update of GBK for Unicode 3.0 with an extension that covers all of Unicode. It has the following general features:
GB 18030 character assignments are backwards compatible with the GB 2312-1980 standard and the GBK specification.
The mapping table between GB 18030 and Unicode is backwards compatible with the one between GB 2312-1980 and Unicode, and with some exceptions (with the one between GBK and Unicode), most of the changes compared to the GBK mapping table are due to updates for Unicode 3.0.
GB 18030 specifies a mapping table that covers all Unicode code points. It is functionally similar to a UTF (Unicode Transformation Format) while maintaining compatibility of GB-encoded text with GBK and GB 2312-1980.
