[Protected Mode] DB bit descriptor

1.DB located on 22 bit

Have an impact on the following three conditions:

Case 1: impact on the CS segment

　　　　D = 1 32-bit addressing mode

　　　　D = 0 16-bit addressing mode

　　　　Addressing change the prefix 67

Case 2: Impact on SS segment

　　　　D = 1 Stack implicit access instructions (such as: PUSHI POP CALL) using 32-bit stack pointer register ESP

　　　　D = 0 Stack implicit access instructions (such as: PUSHI POP CALL) 16-bit stack pointer register SP

Case three: expand down data segment:

　　　　D = 1 on the line segment 4GB

　　　　D = 0 on the line segment is 64KB