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Here we collect some general (and by no means complete) information about usage and policies of a HPC cluster.

==Structure of a HPC cluster==

[[File:Logical structure HPC cluster.png|500px|top]]

The '''structure of a HPC system''' is sketched in the picture above. 
These are the main logical building blocks:

* a ''login node'' is exposed to users for access (typically via <code>ssh</code>), 
* a dedicated ''scheduler'' (the ''queuing system'') dispatches computational jobs to the ''compute nodes''
* computation happens therefore asynchronously (in batch mode), and not on the login node.
* a specific ''software environment'' is provided on the login node and on the compute node to run parallel jobs
* the above cluster structure is used from commodity local machines to large scale HPC architectures (as shown below for the Summit machine at Oak-Ridge Natl Lab (ORNL), TN, USA)

[[File:Summit ORNL.jpg|300px|top]]

==Connecting==
Unless other means are provided, you typically connect using the <code>ssh</code> protocol.

From a shell terminal or a suitable app:

  ssh -Y <user>@<machine_host_name>  or
  ssh -Y -l <user> <machine_host_name>

  <user>:  Unix username on the cluster login node