BASED_CODE的含义和用法

[litian]

我看了msdn关于BASED_CODE的讲解，但不是很懂，它的讲解是：
Under Win32, this macro expands to nothing and is provided for backward compatibility. Under 16-bit MFC, the macro ensures that data will be placed in the code segment rather than in the data segment. The result is less impact on your data segment 不知道是什么意思？请问在什么场合用？
我看到这样一个例子：
static char BASED_CODE filter[] = "BMP Files (*.bmp)|*.bmp||";
CFileDialog opendialog( TRUE, 0, 0, OFN_FILEMUSTEXIST, filter, this );
if ( opendialog.DoModal() == IDOK )
{....
}

这些代码在打开一个BMP文件的代码段中，哪位大侠能讲解一下？