A survey of computer hardware description languages in the U.S.A.

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.