Ideas for the Introduction lesson

[lgorenstein]

Couple comments on the "00-why-hpc" introduction lesson.

• <trivial, but> We are very used to calling our machines "clusters". But this jargonism term needs to be introduced before first use ("An HPC system, often informally called "cluster" because it is made of many individual computers", etc).
• Both Key Points of the lesson are concentrating very much on the distributed/parallel character of the clusters ("...your computations require more than one computer" and "Because a cluster is distributed, it is only useful for certain types of computational problems"). This feels like a bit too general of a statement, and it effectively contradicts one of the declared target audience groups (those who "already write and run domain-specific software on "smaller" computers, and now need to scale up/out"). I would argue that even the most serial code can benefit from being ran on a cluster node vs Alice's laptop - just because it would not swap as much due to sheer amount of the node's RAM :)

Additionally, I think that there needs to be a "01-what-is-a-cluster" (a.k.a "General anatomy of an HPC system") section as part of the introduction lesson. Nothing major, but a visual diagram and a narrative along the lines of "The cluster is made of login nodes, compute nodes, fast interconnect fabric, scheduling system and attached storage. We will cover each of them in details later, but here's an overview how it all plays together".

Having this general overview before delving into specifics of each individual subsystem would create a good reference point, especially for people with less technical backgrounds.

[ChristinaLK]

thanks @lgorenstein. We're migrating content from here to hpc-carpentry/hpc-intro and I'll move the relevant concerns to an issue in that repo.