Introduction

Parallel Virtual Machine

PVM is a software package that permits a heterogeneous collection of serial, parallel, and vector computers on a network to appear as one large computing resource.

PVM allows us to use the combined power of a number of computers.
PVM is a virtual computer that allows multiple supercomputers to be linked together to achieve Grand Challenge performance.
PVM is an educational tool that allows institutions without access to parallel computers to teach courses in parallel computing.

Major Features of PVM

Easy to install.
Easy to configure.
Each individual's configuration can overlap other users' PVMs without conflict.
Easy to write programs with the use of a standard message-passing interface library.
Supports C and Fortran-77 applications.
The PVM package only requires a few Mbyte of disk space.

Heterogeneity

PVM supports heterogeneity at three levels.

Application: Subtasks can use the architecture best suited to their solution.
Machine: Computers with different data formats, different architectures (serial or parallel), and different operating systems.
Network: Different network types; for example. FDDI, Ethernet.

Portability

PVM currently runs on:

  80386/486 with BSDI		Alliant FX/8
  DEC Alpha/OSF-1		BBN TC2000
  DEC Microvax			Convex 
  DECstation			Cray YMP and C90
  DG Aviion			IBM 3090
  HP 9000/300			Intel Paragon
  HP 9000/700			Intel iPSC/2
  IBM RS/6000			Intel iPSC/860
  IBM/RT			Kendall Square KSR-1
  NeXT				Sequent Symmetry
  Silicon Graphics IRIS		Stardent Titan
  Sun 3				Thinking Machines:
  Sun 4, Sparc			CM-2, CM-5
				Meiko CS-2

Portability

Version 3 is portable to non-Unix machines and multi-processor computers
Versions running and available on iPSC/860, Paragon, CM-5, and CS-2.

The PVM System

The System is composed of:

Pvmd3 daemon program that
- Runs on each host of the virtual machine
- Provides inter-host point of contact
- Authenticates tasks
- Executes processes on the hosts
- Provides fault tolerance
- Is mainly a message router, but is also a source and sink of messages
Libpvm programming library that
- Is linked with each application component (program)
- Contains the PVM message passing functions
Application components
- Written by users in PVM message-passing calls
- Are executed as PVM `tasks'

Changes from v2 to v3

New features in PVM include:

TIDs that provide an efficient method of identifying processes in PVM . Since TIDs must be unique across the entire virtual machine, they are supplied by the local pvmd and are not chosen by the user
Dynamic configuration of the virtual machine to enable addition and deletion of hosts during execution
Pvmds with fault detection, thereby enabling fault-tolerant applications to be built
Console not built into pvmd, and is therefore a normal task
Portability to multi-processors. PVM3 is designed to use native communication calls within a multi-processor computer
Multiple message buffers to allow messages to be saved and forwarded

Programming Concepts

Some terminology associated with PVM programming:

Host: A physical machine; for example, Unix workstation or parallel computer
Virtual machine: Combination of hosts running as a single concurrent computational resource
Process: A program, data stack, etc... For example, a Unix process or a node program
Task: A PVM process - the smallest unit of computation.
TID: A unique (per virtual machine) identifier associated with each task
Message: An ordered list of data sent between tasks

Submitted by Mark Johnston,
last updated on 12 January 1995.