In most compute environments today, users have a personal desktop (running the Windows operating system) and have access to a remote cluster to perform their simulations.  The remote cluster usually consists of a few to hundreds of powerful machines that are used by many different users.  This is very efficient for running your CFD-ACE+ simulation, but what about grid generation, monitoring the progress of the simulation, or post processing the results on the remote machine?  These are all interactive applications and require a user interface to use.  In this case, it may be necessary to display the application, such as CFD-VisCART, back to your desktop using an X server.   

Why use an X server to display back to your desktop?  Most desktops have a limit of 2Gb of RAM, which limits the size of the model that can be run on your machine.  Another reason is that you are working with other applications on your desktop and do not want to slow your machine down.  While these are probably the most common reasons to use a remote machine, there could be other situations where it would be useful to display remotely.

What tools are available for displaying remotely?  Cygwin is a free tool that provides you with a Unix-like environment on a Windows operating system.  Cygwin provides the user with a Unix-like shell where you can execute Unix commands, such as ls, grep, find, etc., as well as execute shell scripts.  Also included in Cygwin is startx, which allows you to display applications remotely to your desktop.  

 Using startx:

To use startx, the first thing you need is Cygwin, which can be found here.  Once you have downloaded Cygwin and installed it on your machine, you are ready to use startx.  

From a Cygwin shell, simply type startx in the command line.  This will start an X terminal, which will be used for remote display.  In the X window, type "xhost +", as shown in Figure 1.  The xhost command is used to add and delete hosts (remote machines) which are allowed to the X server.  The "+" argument to the command simply allows all hosts to connect to the X server.  If you only want to allow a specific machine to connect to the X server, you need to specify the host name for the machine after the xhost command.  For example, if we need to connect to a machine named "kramer", the command would be "xhost kramer".  

Figure 1.  The xhost command in the X terminal.

Now that all hosts have been added, login to the remote machine using telnet or ssh.  In this example, ssh is used to connect to the remote machine, as shown in Figure 2.

Figure 2.  Connect to the remote machine using ssh.