The Mainframe is a large structure that stores and secures most of the Chinese's special weaponry and technology, most prominently created by their lead scientist, Yunru.
Also, it is the old core of VOLKNET, the experimental, yet advanced artificial intelligence of the Foehn Revolt.
In Thread of Dread, the Mainframe makes its appearance inside Yunru's massive base. It is surrounded by numerous Chinese soldiers and defenses while also being covered by a special type of wall. It must be captured to obtain the Chinese's most powerful weaponry, the Centurion tech, and will be used to locate Yunru and her Centurion in the battlefield. It is later revealed that the Mainframe housed the final MIDAS warhead that was detonated and eradicated all the forces situated in the Kashmir facility.