Attributes are meta properties attached to types or objects. Some attributes are simulation-only, others help avoid hard-coded constants. List is still incomplete, new sections regularly added
Data types are attributes that help VHDL compiler understand data treatment. VHDL allows both standard and user-defined data types. IEEE library is most popular standard library containing extensive data types
Numeric_Std package is recommended over Std_Logic_Arith. Length VHDL attribute should be used for portability
VHDL has major standards from 1987 to 2018, with VHDL-2008 being recommended for new designs. Designs consist of entity and architecture parts, similar to verilog modules. Components are designed as hardware, not computer programs
Testbenches consist of non-synthesizable VHDL code generating inputs and checking outputs. Architecture includes stimulus block generating inputs and output checker. Testbenches can be written in separate files or combined in single file
Logic gate performs Boolean functions on binary inputs to produce single output. Can be ideal or non-ideal physical devices. Primary building methods use diodes or transistors as electronic switches. Modern logic gates primarily made from MOSFETs