Glossary

New to high-performance computing? This page explains the terms you'll meet most often across the manual. Terms are grouped by theme; acronyms also appear as hover tooltips throughout the rest of the site.

The basics

CRCD Ecosystem
The complement of CRCD infrastructure, including hardware, software, domain experts and services
Resource Allocation
An allotment of computing time and/or data storage quota
HPC (High-Performance Computing)
Using many connected computers together to run computational work that is too large or slow for a single desktop or laptop.
Cluster
A large collection of connected computers ("nodes") that work as one system. CRCD runs several clusters tuned for different workloads — see Hardware Profiles.
Node
A single computer within a cluster. Nodes come in two kinds below: login nodes and compute nodes.
Login node
The gateway machine you land on when you connect. Use it to edit files, manage data, and submit jobs — not to run heavy computation. See Login Nodes.
Compute node
A worker machine where your jobs actually run. You don't log into these directly; the scheduler assigns them to your job.

Hardware

Core (CPU core)
A single processing unit within a node. A job asking for "16 cores" reserves 16 of a node's cores to run in parallel.
Thread
A stream of execution within a program. Many programs run one thread per core; some run several.
GPU (Graphics Processing Unit)
A specialized processor that accelerates AI/ML and certain simulations. See the GPU cluster.
RAM (memory)
The fast working memory a job uses while running, requested separately from cores. Running out of memory is a common cause of failed jobs.

The CRCD clusters

SMP cluster
Symmetric Multi-Processing — for jobs that run on a single node and share one pool of memory. See SMP.
MPI cluster
For tightly coupled jobs that span multiple nodes using the Message Passing Interface. See MPI.
HTC cluster
High-Throughput Computing — for many independent single-node jobs, widely used for genomics and health-sciences work. See HTC.
GPU cluster
Nodes equipped with GPUs for accelerated computing. See GPU.
TEACH cluster
Resources set aside for courses and teaching. See TEACH.
VIZ
A graphical Linux desktop environment for visualization and GUI applications. See VIZ.

Jobs and scheduling

Job
A unit of work you submit to a cluster — a script plus the resources it needs (cores, memory, time).
Batch job
A job that runs unattended: you submit a script and the scheduler runs it when resources are free. Most work runs this way. See Slurm Batch Jobs.
Interactive job
A session on a compute node where you type commands live, useful for testing and exploration. See Interactive Jobs.
Scheduler
The software that decides which jobs run where and when, balancing everyone's requests fairly.
Slurm
The specific scheduler ("workload manager") CRCD uses. You interact with it through commands like sbatch, squeue, and scontrol. See the Slurm Overview.
Partition
A named subset of a cluster's nodes that jobs are submitted to, often grouped by hardware type or purpose.
Preemptible Partition
A low-priority partition that runs on idle resources at no service-unit cost, but whose jobs can be preempted (interrupted) when higher-priority work needs the nodes. See Preemptible Partitions.
Walltime
The real-world clock time a job is allowed to run before the scheduler stops it. Request enough, but over-requesting can delay when your job starts.
Allocation
The share of computing resources granted to your research group, which your jobs draw from.
Service Unit (SU)
The accounting unit used to measure and charge cluster usage (roughly, one core running for one hour). See Service Units.

Software

Module
A pre-installed software package you load into your environment on demand with module load, rather than installing it yourself. See Discovering Software.
Lmod
The tool that manages modules, letting you search (module spider), load, and unload software versions cleanly.
Spack
The build system CRCD uses to install and organize software on the current (RHEL 9) clusters, which is why modules are named the way they are.
CRC wrappers
CRCD's crc-* helper commands (for example crc-interactive) that simplify common Slurm tasks. See CRC Wrappers.

Storage

Home directory (ihome)
Your personal space on the clusters (under /ihome/), shared across all nodes and backed up. Good for code and small files, not large I/O. See File Systems.
Scratch space
Fast temporary storage for the heavy read/write of a running job. Not backed up and periodically cleared, so move results out afterward. See Utilizing Scratch Space.

Getting connected

PittNet
the internal University network

Firewall :A network security device that monitors and filters incoming and outgoing network traffic based on an organization's previously established security policies

VPN (Virtual Private Network)
A secure network connection (Pitt's is GlobalProtect) required to reach the clusters from off campus. See Getting an Account.
SSH (Secure Shell)
The protocol for connecting to a login node from a terminal. See SSH using a terminal and Passwordless SSH.
Open OnDemand (OOD)
A web portal for using the clusters through your browser — files, notebooks, and interactive apps with nothing to install. See Open OnDemand.