Using _seg causes a pointer to become a storage place for a segment value, rather than an OFFSET ( or a segment/offset ). For instance, if "int _seg *x" contains the value 0x40, then when you USE "*x", the value pointed to will be at segment 0x40, offset 0. If you add a value to the pointer, the value is MULTIPLIED by the size of the pointer type. That new value is USED as an offset, and is combined with the segment value contained in the pointer. For instance, 

int _seg *x; 

int value; 

x = (int _seg *)0x40; 

value = *(x + 20); 

value is assigned the value of the integer at 0x40:0x28 

(Remember, 20 * sizeof(int) = 40 = 0x28).

Using _seg causes a pointer to become a storage place for a segment value, rather than an offset ( or a segment/offset ). For instance, if "int _seg *x" contains the value 0x40, then when you use "*x", the value pointed to will be at segment 0x40, offset 0. If you add a value to the pointer, the value is multiplied by the size of the pointer type. That new value is used as an offset, and is combined with the segment value contained in the pointer. For instance, 

int _seg *x; 

int value; 

x = (int _seg *)0x40; 

value = *(x + 20); 

value is assigned the value of the integer at 0x40:0x28 

(Remember, 20 * sizeof(int) = 40 = 0x28).