This is illustrated by the following example that shows a batch server for parallel applications. As mentioned in the introduction, quite a lot of distributed applications perform well on today's workstation clusters, because they are not very communication intensive. But if several of these parallel applications should be simultaneously executed on an existing workstation cluster, the communication channel might become the bottleneck, because it cannot satisfy the communication requirements of all applications together.
Every single application runs in one individual column of workstations.
Therefore, this application can use the corresponding communication channel exclusively. The horizontal network channels can be used for different global tasks within the cluster, e.g. NFS, distribution of applications, collection of results, management operations, etc. Furthermore, the software must be able to manage inhomogeneous cluster components. The workstations can for example differ in performance or may be equipped with special co-processors for image processing, etc. But also the communication network can be built up with different types of network technologies.