What are "extended integer types"?

Extended integer types are implementation-specific integer types that are provided as an extension. Because almost everything about such extensions is implementation-defined, the standard can’t say much about them. However, a C++09 proposal provides a framework for implementing such extensions in a way that doesn’t interfere with the behavior of standard compliant programs.

you should refer this,which covers everything about extended integer types.

An example of the extended integer type is the __int64 64-bit signed integer type defined by MS Visual C. While this type is obviously an integral type, in older versions of MSVC it could not be obtained as int, long int, nor long long int. (MSVC added support for long long int in the meantime.)