The ModelSim-Altera Edition software is licensed to support designs written in 100 percent VHDL and 100 percent Verilog language and does not support designs that are written in a combination of VHDL and Verilog language, also known as mixed HDL. Mixed HDL support is available in the PE and SE versions of ModelSim from Mentor Graphics. ModelSim-Altera Edition only supports Altera gate-level libraries. The ModelSim-Altera Edition software includes all ModelSim PE features, including behavioral simulation, HDL testbenches, and tool command language (Tcl) scripting. However, the simulation performance of the ModelSim-Altera Edition software is slower than that of the ModelSim PE and SE software.