Aspen Plus 2006 is based on the Intel Fortran 9.0 compiler and Microsoft Visual Studio .NET 2003. This is a change from the past several versions of Aspen Plus, which used Compaq Visual Fortran instead. Aspen Plus has moved away from Compaq Visual Fortran because this compiler is no longer supported by its manufacturer and may be difficult for some customers to obtain. It is possible to continue using Compaq Visual Fortran with Aspen Plus 2006, with certain limitations. See the following section for information on how to configure Aspen Plus 2006 to use this compiler, and the text immediately below for details on these limitations. If you used the Compaq Visual Fortran compiler previously, please be aware of the following issues in upgrading to Aspen Plus 2006 andor the Intel Fortran compiler: • Object files (.OBJ) and static libraries are not compatible between Compaq and Intel compilers. If you move to the Intel compiler you will need to recompile any object files from their source code using the new compiler. • Use DLLs (dynamic or export libraries) for maximum compatibility between code compiled with different compilers. • READs and WRITEs to Fortran IO units opened by code compiled by a different compiler will not work. Aspen Plus 2006 opens its predefined units (such as the history file and the control panel) using the Intel compiler, so any code compiled by the Compaq compiler will no longer be able to write to these units. Important: Installing the new compiler software can prevent past versions of Aspen Plus (2004.1 and earlier)