Abstract: Trust base in operating systems(OS),or TBOS for short,is defined as the set of all elements in an OS that provides support for the trustworthiness of a computing platform.Designing philosophy of TBOS is established.An architecture of TBOS is proposed.The focus is put on presenting key concepts of key TBOS components.Abilities of isolation and interaction and characteristics of dynamic extension of TBOS are also introduced.Moreover,key issues concerning the implementation of TBOS are discussed.