HPC Terminology

This page contains a non-exhaustive list of terms that are important for getting a basic understanding of an HPC system and how to use it.

Users of the Palma2 HPC cluster of the University of Münster should also refer to the Palma2 Wiki.

High Performance Computing (HPC)

Local machine

Your local desktop or laptop computer.


A group of computers (so-called nodes), connected by a network to function as if they were one, large computer with a lot of resources (CPU, GPU, RAM, disk space, …).


One of the computers of a computer cluster.


The slot which hosts the CPU and connects it with the motherboard. A single motherboard might have multiple sockets.


The Central Processing Unit (CPU), or simply processor, does the arithmetic and logic and controls the rest of the computer.

Physical Core

A physical (i.e. really present) subunit of the CPU.

Logical Core

A software abstraction that allows you to run multiple threads on one physical CPU core. For instance, with Intel’s hyper-threading technology you can run two threads on one physical core. In short, the number of logical cores is the number of physical cores times the number of threads that each physical core can run (quasi-)simultaneously.


A set of instructions to be executed by the CPU.


A running program.


The graphics processing unit (GPU) processes the data to be shown on a display. GPUs have hundreds of cores and can therefore be used to execute massively parallel programs.


Random Access Memory (RAM), or simply memory, is the main memory (German “Arbeitsspeicher”) of a computer.

Hard Disk Storage

The storage that holds all your data (German “Festplattenspeicher”).

Slurm Workload Manager

The Slurm (Simple Linux Utility for Resource Management) Workload Manager is a popular software package that organizes and schedules the jobs of different users in such a way that the HPC cluster is optimally used and each user gets a fair amount of computing time.


Slurm uses the terms Core and CPU interchangeably depending on the context. For instance, the sbatch option --cpus-per-task is actually specifying the number of cores per task. Whether these are physical or logical cores depends on whether the cluster administrator has enabled threading or not. To get an overview of the resources available on your cluster you can run sinfo --format "%12P | %.22g | %.12l | %.6a | %.15F | %.23C | %.5c | %.8X | %.6Y | %.8Z | %.8m | %.15f | %.15G".


A waiting line in which you can submit your jobs. Usually, one or more nodes are assigned to a partition. If you submit a job to a partition it will only run on the nodes assigned to this partition. However, one and the same node can be assigned to multiple partitions.


A self-contained computation that is submitted to a partition. A job might consist of multiple steps (e.g. a preparation step, the actual computation and a clean-up step) which in turn consist of one or more tasks that run on one or more CPUs (for an example see https://stackoverflow.com/a/46532581).


A self-contained part of a job.


A single run of a single program.

Parallel Computing

Terms that you will probably come across when you perform computations on multiple CPUs:

Distributed-Memory System

A computer with multiple processors in which each processor has its own private memory. Processors cannot access the memory of other processors.

Shared-Memory System

A computer with multiple processors that all share the same memory.


The Message Passing Interface (MPI) is a message-passing standard that allows multiple processes that run in separate memory spaces to exchange information. Hence, MPI allows you to run a program in parallel on different CPUs in a distributed-memory system. It can also be used on shared-memory systems but usually this causes some overhead compared to using OpenMP.


Open Multi-Processing (OpenMP) is an Application Programming Interface (API) that allows you to run a program in parallel on one or more CPUs in a shared-memory system.

Usually, all CPUs on one node share the same memory but different nodes have different memory spaces. Hence, if you want to run your program on multiple nodes, you must use MPI for communication between processes on different nodes and you can use OpenMP for communication between processes/threads on the same node (this would be a so-called hybrid MPI-OpenMP job).

MPI ranks can be identified with Slurm tasks and OpenMP threads correspond to the number of cores per task (sbatch’s --cpus-per-task option). But this is just a rule of thumb. There exists no strict connection.