q about gb 2312/gbk

Hello, I have two questions about GB* simplified-Chinese charsets:

1. There are two entries for GB 2312:
1.a)
Name: GB_2312-80                                        [RFC1345,KXS2]
MIBenum: 57
Source: ECMA registry
Alias: iso-ir-58
Alias: chinese
Alias: csISO58GB231280

1.b)
Name: GB2312  (preferred MIME name)
MIBenum: 2025
Source: Chinese for People's Republic of China (PRC) mixed one byte, 
        two byte set: 
          20-7E = one byte ASCII 
          A1-FE = two byte PRC Kanji 
        See GB 2312-80 
        PCL Symbol Set Id: 18C
Alias: csGB2312

How are they different?
The second one is clearly the commonly used MBCS charset.
Is the first one the DBCS-only part for ISO 2022, or is it also MBCS? Please clarify.


2. I cannot find a registration for GBK (Microsoft 936).
Am I just missing it?

markus