MPP vs. workstations?

 Joe Leonard write:
 >1) I think most/all of the Comp Chem codes run on shared-memory MIMD
 I think there have been a number of hypercube implementations, no?
 We have a parallel version of Hondo running on an IBM Power Visualization
 System.  The PVS does have a global memory, but it's used primarily as a
 disk and communications buffer.  The code runs in each processors' local
 memory.
 >2) A significant problem slowing the spread of mpp machines is the relative
 >lack of tools to assist/facilitate the port.  Vector machines have had 8-10
 Ain't that the truth?  We programmed down to the bare system call, rather
 than using tools like TCG or Linda, and had no preprocessor available.
 The housekeeping one has to take care of just in copying common blocks
 around is bothersome enough.  This buys us good performance in some
 areas, such as gradients, but actually makes the fine tuning much more
 difficult.
 Another area, that might be mostly of interest to our group, is parallel
 IO.  The PVS has a HiPPI-connected RAID sub-system.  We've been able to
 sustain 55MB/s global memory to disk bandwidth for "toy" C programs,
 and
 45 MB/s from (multi) processor local memory to disk for real Fortran codes.
 So for us direct SCF is not a priority.  The catch is, the RAID doesn't
 support a UNIX file system, and in fact doesn't support much of a file-
 system at all!  We had to write our own Fortran IO library and change
 all READs and WRITEs to CALLs to the library.  This was more of a
 learning experience than an attempt to make a production code, but
 I think there will remain data-intensive applications and some better
 paradigms for high performance parallel IO remain to be developed.
 >micro's basically killing everything in site.  It's a great time to be a
 >software developer, but it's tough living on the hardware side.  This is
 >a real problem, because who will enable us to use the new machines if
 there's
 >nobody on the inside with application-apecific expertise?
 Our thoughts exactly!
 --
 David J. Heisterberg (djh-0at0-ccl.net)       What men value is not rights
 The Ohio Supercomputer Center            but privileges.
 Columbus, Ohio                             -- H.L. Mencken