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Abstractual an open source cloud solution capable of HPC and extreme scale and distribution
Autovectorization A technique used by a compiler to take a sequential code and replace sequences of operations by vector instructions that can be executed on a vector processor.
Batch queue A subsystem managing an HPC's workload. Users submit batch jobs to the queue to be executed when resources are available. See also Scheduler and Resource Manager
Beowulf A cluster of Linux based PC's, using commodity hardware and open source software.
BLAS Basic Linear Algebra Subroutines -- a kernel of linear algebra routines usually heavily optimised by a CPU's vendor to make use performance features of that CPU. Used extensively by Lapack Bus Connection between CPU and memory and/or other peripherals.
C,C++ High level programming languages widely available on HPC computers, standardized by the ANSI committee. C is almost a subset of C++.
C++ offers features such as object oriented programming, generic programming and operator overloading.
Cache Small piece of fast, expensive memory between the CPU and main memory
Cache Coherency Hardware support on SMP systems to ensure that each processor's cache has a consistent view of the data in main memory
Caos Linux An open source RPM managed Linux that focuses on HPC and cloud. Not a fork of Enterprise Linux, but designed from the ground up for scalability
Checkpoint The state of a running program written to a file to allow the program to restart a calculation from the point saved in the checkpoint file.
Classdesc A technology for passing objects between processes, or saving objects to files in C++. See http://parallel.hpc.unsw.edu.au/classdesc for more details.
Cluster Multiple complete computers connected via a network, and operated as a single system.
Compiler A program that translates high level source code into object code
CPU Central Processing Unit
Cygwin A suite of open source unix-like development tools for MS Windows based computers
Debugger A tool to interactively stop a program, step the program line by line and examine contents of the program's data
Distributed Memory A parallel computer whose processors' main memory is physically separated from each others -- contrast with shared memory
Ensemble Calculation Multiple copies of a simulation run with a different sequence of random numbers, and the results averaged to produce a more accurate statistical measure.
Equilibria highly-effective open source load balancer for cloud or web use
Flop Floating point operations per second. Addition, Subtraction and Multiplication are considered atomic floating point operations, but Divisions usually performed by combining multiplications and additions as in the long division algorithm
Fortran A very popular high level language used with HPCs. Standardised by the ANSI committee, the standards are known by the year in which the standard was released: Fortran77, Fortran90, Fortran95.
Generic Programming A technique for writing code supporting multiple types. Also known as a template. Supported in C++, and coming soon to Java.
Granularity In parallel computing, granularity is a qualitative measure of the ratio of computation to communication, such as Coarse: large amounts of computational work are done between communication events and Fine: small amounts of computational work are done between communication events
Hadoop an open-source implementation of frameworks for distributed computing and data storage
HDFS Hadoop File system.
High Performance Computer A computer whose performance exceeds that of standard workstations by at least an order of magnitude.
High Performance Fortran A distributed memory programming language based on Fortran95, abbreviated with HPF
Hyperthreading A technique of running multiple threads on a CPU so that the CPU doesn't stall when waiting for data from memory.
Interpreter A program that executes high level source code without translating it into object code first.
Java An interpreted object oriented high level language widely deployed on the Internet, but not too popular for high performance computing due to performance reasons.
Java Grande is an attempt to promote Java for High Performance Computing.
Lapack A highly efficient, open source linear algebra library widely available on high performance computers. Functions include solutions to linear equations and eigenvectors. Depends heavily on BLAS.
Latency The amount of time it takes to complete an operation - eg the time for a data packet to travel between two computers. cf bandwidth
Library A collection of precompiled (as in object code) routines that can be linked to a program.
Linker A program that links together independently compiled pieces of object code (including those residing in libraries into a single executable file).
Maui An open source scheduler
Multiple Data -- a parallel computer with each processor working independently on its own data -- cf SIMD, SPMD
MPI Message Passing Interface -- an industry standard interface for programming distributed memory computers.
Object Code Compiled machine code, that may contain references to code and data in other object files.
Object Oriented Programming A technique for attaching code to pieces of data (the combination called an object). Whilst this can be done with any language, it is easiest in languages that explicitly support OOP.
OpenPBS An open source scheduler
OpenMP A standard interface for distributing work across threads of a shared memory computer.
Open Source A program whose source code is available to the general public.
Operator Overloading A technique for redefining the operator symbols (+,-,*,/, etc) to do whatever the programmer wants on arbitrary typed data.
Optimiser Part of a compiler that performs a suite of basic code optimisations automatically.
Paging Transferring data from main memory to disk as part of the virtual memory subsystem.
Parallel Computer A computer having multiple CPUs
Parametric Calculation Multiple copies of a program run, each with a different set of input parameters
PBS An open source batch queuing system
Perceus An open source provisioning systems that powers many of the worlds top supercomputers
Posix Threads A standard interface for controlling threads on a shared memory computer
Process A distinct task having its own state and address space. cf thread
Profiler A tool used to analyze which parts of a program are most computationally significant.
PVM Parallel Virtual Machine -- an interface for programming distributed memory computers.
RAM Random Access Memory -- the main memory is made out of RAM, so RAM sometimes stands for the main memory
Red Hat Linux An open source but commercial RPM managed Linux that focuses on Enterprise. Red Hat is a trademark of Redhat.
Screen An open source application that allows processes to remain running even if a user is disconnected or logs out.
Scheduler A program that controls which batch job runs next, when a resources are available.
Shell An interpreter used for executing commands typed at a keyboard, or scripts.
SIMD Single Instruction, Multiple Data -- A parallel computer performing the same operation, on different items of data at the same time. cf Vector, MIMD, SPMD
SLURM An open source scheduler
SMP A shared memory parallel computer (sometimes symmetric multiprocessor if talking about hardware)
Software Pipelining A technique employed by a compiler for improving the performance of a CPU. Given operations that are decomposed into a sequence of steps that use distinct pieces of hardware, software pipelining arranges for the next operation to be started before the first finishes, increasing the amount of hardware used at any one time, and improving the CPUs throughput.
SPMD Single Program, Multiple Data The same program is executed on different items of data, but the operations need not be performed in lockstep (i.e. at each step (global clock tick) all processors execute the same instruction, each on a different datum) as in SIMD. MPI is an SPMD programming environment, whereas PVM is full MIMD.
SDRAM : A faster version of DRAM, mostly employed for main memory SRAM
Static RAM : A fast, expensive RAM often used for vector computers or caches
ssh Secure Shell A secure replacement for Telnet that utilizes encryption for computer to computer communications.
Standard Template Library A standard library of containers (aggregates of objects of arbitrary type, such as vectors, lists, sets etc) for C++. Make extensive use of generic programming.
Stack An area of memory used to store arguments and local variables of subroutines and functions. As a subroutine is called, a stack frame is pushed onto the stack, allocating memory for these variables. As the subroutine exists, the stack frame is popped off, destroying the contents of these variables.
Superlinear A program that actually performs better than $n$ times faster than sequential, when run on $n$ processors. Usually due to cache effects (total cache also increases with processor count).
Swapping Transferring data from main memory to disk as part of the virtual memory subsystem.
Threads Independent tasks executing the same code in the same address space. Each thread has its own stack, so local variables are thread private. Global variables are shared.
Torque An open source scheduler forked off of OpenPBS
Vector Computer A computer implementing instructions that work on a vector of data at once. This may be implemented as a pipeline (each operation is further decomposed into steps that each run on their own hardware), or as a SIMD processor. Vector supercomputers do not have a cache, but have very fast main memory instead, consequently outperforming commodity processor.
Virtual Memory Address space is divided up into chunks called pages. A page needs to be in physical memory when accessed by the CPU, but may be stored on disk if not needed for a while, thus freeing physical memory for other processes that need it.
Warewulf An open source HPC solution
Workstation A networked desktop computer running a modern multitasking operating system such as Unix or MS Windows.
X windows A graphical windows interface where the program performing the graphics (the X-windows client) may be running on a different computer to where the user is seated (called the X-server). The client and server communicate using the X libraries protocol (Xlib).
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