A registry can store different types of values in various formats. These Registry Value Types are listed here. When you store data under a registry value, for instance by calling the RegSetValueEx function, you can specify one of the following values to indicate the type of data being stored. When you retrieve a registry value, functions such as RegQueryValueEx use these values to indicate the type of data retrieved.
The following registry value types are defined in Winnt.h.
Read more at Microsoft MSDN Registry Value Types.