# 2.3.2. Building OpenFAST on Windows with CMake and Cygwin 64-bit¶

WARNING: This build process takes a significantly long amount of time. If GNU tools are not required, it is recommended that Windows users see one of the following sections:

## 2.3.2.1. Installing prerequisites¶

1. Download and install Cygwin 64-bit. You will need to Run as Administrator to complete the installation process.

• Choose Install from internet
• Choose the default install location
• Choose Direct connection
• See next step for select packages. Alternately, you can skip this step and run setup-x86_64.exe anytime later to select and install required software.
2. Select packages necessary for compiling OpenFAST. Choose binary packages and not the source option.

• Choose Category view, we will be installing packages from Devel and Math

• From Devel mark the following packages for installation

• cmake
• cmake-doc
• cmake-gui
• cygwin-devel
• gcc-core
• gcc-fortran
• gcc-g++
• git
• make
• makedepend
• From Math mark the following packages for installation

• liblapack-devel
• libopenblas
• To run the test suite, install these optional packages from Python:

• python3
• Python3-numpy
• Click Next and accept all additional packages that the setup process requests to install to satisfy dependencies

3. It is recommended that you reboot the machine after installing Cygwin and all the necessary packages.

## 2.3.2.2. Compiling OpenFAST¶

From here, pick up from the Linux with CMake instructions at CMake with Make for Linux/macOS.

## 2.3.2.3. Other tips¶

• If you would like to run openfast.exe from the cmd terminal, then you must add the C:\cygwin64\lib\lapack and C:\cygwin64\home\<USERNAME>\software\bin to your %PATH% variable in environment setting. Replace <USERNAME> with your account name on Windows system.

• It is suggested to compile with optimization level 2 for Cygwin. Do this by changing the build mode in the cmake command

cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo