All character set standards that originate in the PRC have designations that begin with "GB".
GB is an abbreviation for Guojia Biaozhun, meaning "national standard".

1. GB 2312-80
The GB 2312-80 encoding contains simplified Chinese characters and is designed for normal use in mainland China. The GB 2312-80 character set standard was established in 1981 to represent simplified Chinese characters.
GB 2312-80 is a coded character set that contains 7,445 characters, including 6,763 Hanzi and 682 non-Hanzi characters.

2. GB/T 12345-90
The GB/T 12345-90 encoding is the traditional Chinese counterpart of GB 2312-80. It is designed for use in mainland China when traditional, rather than simplified, Chinese characters are required.
The GB 2312-80 and GB/T 12345-90 encodings may be regarded as a pair of styles. If a document is created using GB 2312-80, changing the font to GB/T 12345-90 effectively changes the simplifies Chinese characters to their corresponding tradional forms.

3. GBK
The GBK encoding contains both simplified and traditional characters and is designed for use in mainland China when both forms are required in a single font.
With the release of Unicode 2.1 in 1993 a standard named GB 13000.1 was published which contained all the glyphs of Unicode 2.1. To accommodate all additional Hanzi characters specified in GB 13000.1 that are not included in GB 2312-80, a new specification known as GBK was then introduced. GBK is an abbreviation for "Guojia biaozhun kuozhan", which is the Chinese for "Rules/Specifications defining the extensions of internal codes for Chinese ideograms".
GBK contains 21,886 characters including 21,003 Hanzi (101 more than Unicode 2.1 which has 20,902 hanzi glyphs).

4. Big 5
The Big 5 encoding contains traditional Chinese characters and is designed for use in Taiwan and Hong Kong.
Big 5 contains 13,463 glyphs including 13,053 Hanzi.

5. GB 18030-2000
GB 18030-2000 was created as an update of GBK for Unicode 3.0 which defines 6,582 new characters in plane 0 (the Basic Multilingual Plane = BMP).

• It incorporates Unicode's CJK Unified Ideographs Extension A completely (additional 6582 Hanzi).
• It provides code space for all used and unused code points of Unicode's plane 0 (BMP) and its 15 additional planes.

6. HKSCS
The Hong Kong Supplementary Character Set is usually known as HKSCS. For the computer systems used in Hong Kong, the Big 5 and ISO 10646 (Unicode) Standards are usually used. However, those code systems do not contain the particular Chinese ideographs meeting the need for Hong Kong users. As for this aspect, Hong Kong SAR Government and the Chinese Language Interface Advisory Committee cooperated and published the "Hong Kong Supplementary Character Set" in September 1999.
The HKSCS includes 4,818 special Chinese characters that are widely used in Hong Kong. Some are in Big 5, some are in GBK but some are not even in Unicode 3.0.