In this paper, based on the discussion of SASOS (single-address space operating system), as well as its advantages and disadvantages, the concept and principle of NASOS (no-address space operating system) is put forword and a NASOS prototype is discussed. In the NASOS, there is no process virtual address space, instructions access files directly and processes run on files. Compared with SASOS, not only does NASOS have the advantages of SASOS, but also avoids its disadvantages.