An HPC cluster is built out of a few up to many servers that are connected by a high-performance communication network.
The servers are called nodes.
HPC clusters use batch systems for running compute jobs.
Interactive access is usually limited to a few nodes.
A typical cluster contains of these parts:
various system-, hardware-, and I/O-architectures used for supercomputers, i.e. shared memory systems, distributed systems, and cluster systems
physical hardware; chassis/rack, computer system units, interconnect, power., compute node architecture with memory, local disk, and sockets
typical architecture of cluster systems consisting of nodes with different roles (e.g. so-called head, management, login, compute, interactive, visualization nodes, etc.)
Which are functioning as: