Issue No.12 - Dec. (1974 vol.7)
Stephen Y. H. Su , The City College, City University of New York
A digital system can be described at several levels. 1) The highest level is the algorithmic level which specifies only the algorithm to be used for solving a design problem. 2) The second level is the PMS (Processor, Memory, Switch) level which describes a system by processors, memory components, peripheral units, and switching networks. 3) The instruction level describes the instructions of a computer. 4) The register transfer or microinstruction level describes operations among registers. 5) The logic level expresses network in terms of gates and flip-flops. 6) The lowest level is the circuit level which implements gates and flip-flops by circuit elements such as transistors, resistors, etc.
Stephen Y. H. Su, "A survey of computer hardware description languages in the U.S.A.", Computer, vol.7, no. 12, pp. 45-51, Dec. 1974, doi:10.1109/MC.1974.6323411