 Moore (1978) argues that such a duality is one of the three myths of computer science, in that the dichotomy software/hardware has a pragmatic, but not an ontological, significance. Computer programs, as the set of instructions a computer may execute, can be examined both at the symbolic level, as encoded instructions, and at the physical level, as the set of instructions stored in a physical medium. Moore stresses that no program exists as a pure abstract entity, that is, without a physical realization (a flash drive, a hard disk on a server, or even a piece of paper). Early programs were even hardwired directly and, at the beginning of the computer era, programs consisted only in patterns of physical levers. By the software/hardware opposition, one usually identifies software with the symbolic level of programs, and hardware with the corresponding physical level. The distinction, however, can be only pragmatically justified in that it delimits the different tasks of developers. For them, software may be given by algorithms and the source code implementing them, while hardware is given by machine code and the microprocessors able to execute it. By contrast, engineers realizing circuits implementing hardwired programs may be inclined to call software many physical parts of a computing machine. In other words, what counts as software for one professional may count as hardware for another one.