MapWindow has now adopted version 5.1.2 of the TauDEM software. TauDEM, Terrain Analysis Using Digital Elevation Maps, is the main component of the MapWindow Watershed Delineation plugin.
TauDEM version 5 is designed for modern multicore architectures. A multicore CPU has more than one processor: 2, 4, even more. By using an implementation of the Message Passing Interface (MPI), TauDEM version 5 can take advantage of multiple cores, splitting tasks into several processes distributed between them, and speeding up calculations. It is also able (provided your machine has enough memory) to process much bigger DEMs: up to 4GB.
The implementation of MPI used by TauDEM version 5.1.2 is MS-MPI from Microsoft, which is free to download and use.
By default MS-MPI is not installed when you install MapWindow. TauDEM will run without it, in "single process" mode.
You may obtain and install MS-MPI, and we give some instructions below. Then MapWindow will discover that MS-MPI is available, and will take advantage of it. There is no point in doing this unless you have a multicore CPU, and probably not much unless you have large DEMs.
It is possible the first time you run one of the TauDEM executables after installing MS-MPI that you get a TauDEM error, and in the details you will see
Fatal protocol error: check version between Mpiexec.exe, Msmpi.dll, and Smpd.exe.
The way to fix this is to remove or make inaccessible the copy of msmpi.dll that is stored with the TauDEM executables in order to enable them to run without MS-MPI. Go to the directory C:\Program Files\MapWindow\Taudem5Exe (or C:\Program Files (x86)\MapWindow\Taudem5Exe on a 64-bit machine) and rename msmpi.dll to, say, msmpidll (which is better than removal as you can restore it later if necessary).
If you installed MPICH2 for the previous version of TauDEM 5, you can first uninstall it (unless you need it for some other purpose).
Download the MS-MPI installer from here and install it.
Restart the machine (otherwise it will not be able to find the executable mpiexec.exe).
On a 32-bit machine I had a problem installing and running the 2012 version of MS-MPI. If MSMPISetup will not run you need the 2008 version: see below. If the installer runs, after restarting your machine you should check all is OK by opening a command window and running the command mpiexec -help. If there is an error saying that mpiexec is not a valid 32-bit command then download and install the 2008 version of MS-MPI from here.
MS-MPI supports multi-process computations across several machines. So you may get a Windows firewall query as to whether you want to allow the MS-MPI program manager, smpd, access to networks. Since TauDEM only runs multiple processes inside your machine you may Keep Blocking access (Windows XP) or Cancel access (Vista and Windows 7/8, see picture on right) (unless, of course, you are using MS-MPI for other purposes for which it needs network access).