Cygwin is a Linux-like environment for Windows.

It consists of a DLL (cygwin1.dll), which acts as an emulation layer providing substantial POSIX (Portable Operating System Interface) system call functionality, and a collection of tools, which provide a Linux look and feel.

The Cygwin DLL works with all x86 versions of Windows since Windows 95.

It consists of two parts:
- A DLL (cygwin1.dll) which acts as a Linux emulation layer providing substantial Linux API functionality.
- A collection of tools, which provide Linux look and feel.

Cygwin is not a way to run native linux apps on Windows. You have to rebuild your application from source if you want to get it running on Windows.

Cygwin is not a way to magically make native Windows apps aware of UNIX functionality, like signals, ptys, etc. Again, you need to build your apps from source if you want to take advantage of Cygwin functionality.

Note also that, by default, setup.exe does not install everything.

Only the base cygwin distribution is installed by default. When running setup.exe, clicking on categories and packages in the package installation screen will provide you with the ability to control what is installed or updated.

For instance, clicking on the "Default" field next to the "All" category will provide you with the opportunity to install every Cygwin package.

Cygwin can be expected to run on all modern 32 bit versions of Windows, except Windows CE. This includes Windows 95/98/ME/NT/2000/XP.

Be advised that this will download and install hundreds of megabytes to your computer. The best plan is probably to click on individual categories and install either entire categories or packages from the categories themselves.