X200 Ultrabase VS X200 Media Base - Difference

[Lenova25]

What is the diference between he 2 ultrabases for sale when you go to customize a x200 tablet?

The first one available is
Mobile media base
hinkPad X200 UltraBase [add $200.00]

The second is
Notebook expansion
ThinkPad X200 UltraBase ThinkPad X200 UltraBase [add $219.00]

Can someoe explain the difference? Also, do they come with a cd/rw or must that be purchased seperately?

thanks