Register - vector version of a D flip-flop in which all operations on the flip-flops occur simultaneously
"Register transfer level”, RTL - flavor of design that is primarily concerned with how and when data is transferred between the various registers in a digital system
”data-path” designs which require the careful control and timing of the data that is being transferred between registers
Important Points
VHDL can be used to easily implement circuits at the register transfer level. The corresponding VHDL models can be implemented in either structural or full behavioral format
RTL level VHDL models should strive for simplicity in their designs. If the behavioral models in the RTL design become complicated, the chances that your circuit works correctly greatly diminish due to the synthesis of the complicated circuit