The Sun Server X2-8 midplane resides on the internal (front-facing) side of the subassembly module (SAM) and is inaccessible unless the SAM is removed. The midplane provides power and signal interconnects between back side server components and the front-end server components. The midplane and the SAM are considered a single unit. To replace the midplane you must replace the SAM.
Note - The SAM is designated as a field-replaceable unit (FRU).