Re:not Beowulf? (Score 2)

You're making a category mistake. MPI and PVM are message-passing libraries. LINDA is a programming language that uses a tuple space stored in distributed shared memory (see here for more info. HACMP is a completly different beast, see IBM's homepage.

Beowulf != any of these. Beowulf is the idea that one can take commodity, off the shelf (COTS) components and build a powerful machine at a price far less then a comparable commercial offering.

Codes run on Beowulf, and really any parallel machine, typically use MPI, PVM, or custom message passing libraries. The beowulf idea includes the use of MPI & PVM, among other freely available software packages. Codes that run on shared memory machines typicall uses the shared memory device of MPI, shared memory, or pthreads.

For CPU intensive tasks the Beowulf idea is great. Codes that perform lots of disk I/O suffer, as adding higher performance (i.e. SCSI) disks increases system cost greatly. Communication intensive tasks perform the worst on beowulf style clusters compared to commercial computers, as the interconnect on beowulf-style clusters can't compare. For a relatively large increase in cost, one can use Myrinet. With Myrinet bandwidth and latency begin to approach that of the switch found on the IBM SP series of machines.

With high bandwidth, low latency interconnect technologies that scale well (e.g. Myrinet), one can build a cluster that outperforms a comparable commercial offering at, say one quarter to one eigth the price. The difference at that point is software. There's really not alot out there to configure and administer beowulf-style clusters, and commercial implementations of some packages beat the pants off of their freely available counterparts (compilers, for example). Until the software situation changes there is still reason to buy your big iron from IBM, SGI, and Sun.

--Jason