WMPI II is a full implementation of the MPI-2 standard while WMPI only implements version 1.2 of the standard.

Continuous R&D effort is invested in WMPI II to add support for new tools, compilers, interconnectors and to improve performance. These features often also become available in WMPI but there is a difference in the release schedule for WMPI which means there is usually a delay of around six months in new features migrating from WMPI II to WMPI.

Yes. You only need to compile your application for both Windows and Linux you can use nodes running either operating system seamlessly. That is, some processes of an application can run on Windows nodes while others run on Linux nodes - without any restrictions.

A trial license key is automatically sent to the email address with which you registered your user the first time you download WMPI II. If you download WMPI II multiple times you will still only receive the license key once. However, the same trial license key is valid for all versions of WMPI II for Windows and Linux.

The license key is an ASCII file called "wmpi_ii_license.key". You will be prompted for this file during installation so make sure that it is available on the machine on which you wish to install WMPI II. Notice that in some cases an email can be under way for some time. However, in case you have not received a key within a couple of hours, please contact WMPI II support wmpi-support@criticalsoftware.com and we will send you your trial license key.

A trial license key is valid for 4 CPUs and 40 days from the date of download.

WMPI II Windows uses automatic remote installation so that you can add/remove nodes from your cluster easily! You purchase a license valid for 8 CPU's (for example) and it enables you to run WMPI II on a 8-cluster system. You install the license just on a single machine (the License Server). If at any time you wish to upgrade your cluster, just purchase support for more CPUs and you only have to install the license on the License Server. No more maintenance is required.

Neither for WMPI II Linux is a reinstallation necessary. Please contact WMPI support wmpi-support@criticalsoftware.com directly for more information.

A .pg file, or a process group file, specifies which nodes should run which processes. A node can be any machine specified in the .clusterconf file. A .pg file has the following format:

[node1] [number of processes] "[executable] [[arguments]]"
[node2] [number of processes] "[executable] [[arguments]]"
..

If processes are started through mpiexec no .pg file is needed but it can be used. If an application is started as a normal executable, i.e. "myexecutable.exe" for Windows or just "myexecutable" on Linux, it will search for a process group file with the same name, i.e. "myexecutable.pg", in the directory of the executable. If no such file is found, WMPI II will try to load a process group file with the name "wmpi.pg" in the directory of the executable. If this file cannot be found either an error will be reported.

A wmpi.clusterconf file specifies what nodes are available in a cluster. For more information on creating a wmpi.clusterconf file, please refer to the WMPI II documentation. The an application is started through mpiexec the .clusterconf file can be located in any path, since the full path can be given through a command-line argument. If an application is started directly, that is without the use of mpiexec, the wmpi.clusterconf file should be in the same directory as the executable. Alternatively, the WMPI_CLUSTER_CONF_FILE environment variable can be set to point to a wmpi.clusterconf file, which will be loaded in case wmpi.clusterconf is not found in the directory of your executable.

Notice: The .clusterconf file need only be available on the machine from which your WMPI II application is started.

The most common source of this problem is incorrect MPI programming. If, for instance, a node A sends a message to node B of 100 MPI_INTs and node B only sets up a receive with a buffer size of 50 MPI_INTs the message gets truncated. So in case you come across this situation please check that your sends, receives, collective operations, etc. really match as you intended.