Subject: CCL:Summary Choice of computer for G03

From: Ian Hovell <HOVELL:at:cetem.gov.br>
Date: Tue, 13 Jul 2004 13:48:17 -0300

As promised here is a summary to the following question

>I'm looking for the ideal computer for running G03. I was wondering what
>people on the list, when buying a new computer dedicated to Gaussian03,
>would go fo? Would people go for cpu speed, cache memory, RAM or hard disk.
>Where would the emphasise be? And what OS would you opt for. I'm sure these
>questions have been asked for before so if any body can point me to a URL
>they know, okay.
>Thanks for your help and time.

The answers;

I don't believe you will get definite answers to your question. I've seen
people on this list using computers of all kinds, single or multi
processors, Linux, Windows, Mac, etc... running Gaussian. Maybe the most
important question is what kind of simulations do you want to do on this
computer?

Of course, I'd go for the best computer possible, ant that means best CPU,
with large cache,  maximum RAM and a large HD. Especially, if you plan on
doing ab-initio calculations on large molecules, you will need lots of HD
space, and maybe consider a 62 bit processor.

As for OS, I'd definetely go for Linux, unless you choose a multi-processor
computer for which Linux isn't available.

HTH,
          Gustavo Seabra.

Ian, I have grown fond of Mac's again, since OS X is the only operating
system where I can do both professional development in C and Python
alongside Word - all without an emulator and/or dual booting.  The prices
for dual processors are comparable to what Dell has, if not a little cheaper
(list prices, YMMV).
Whatever you get, there are a number of things to consider:
1)	People forget that there are things like memory bandwidth and
disk/IO bandwidth.  Thus, they purchase the fastest processor(s) they can,
and wonder why their jobs don't run as fast as they'd expected.  I'd plan
for 1 job per 1 or 2 processors for maximum efficiency.  If you have to use
integral files, I'd investigate fast disks, SCSI, etc.
2)	Compilers make a HUGE difference.  gcc/g77 are way slower than
machine-specific compilers (Intel/PC or IBM/Mac).  While it costs a little
$$, getting 20-50% faster run-time is a cheap upgrade.  Some compilers also
have difficulties with some parallel libraries, or don't offer them - check
with Gaussian if there's any good or bad purchases.
3)	The safe recommendation is that one should get as much memory and
disk as possible.  See (1) for kinds and/or speeds of disk.  Regarding
cache, I don't know how particular portions of Gaussian relate to cache
hits/misses - they should know this.  Of course, running more than a single
job on the box is quite a bit worse re: cache than differences with a single
job.  And I think people now feel that machines should NEVER page (some turn
off the option in Linux), so lots and lots of RAM is required.
4)	Do you want to be your own system manager?  Do you have access to
one who is competent?  If not, maybe Linux will be a bother - nothing's real
good out of the box as I understand things.  I run off-the-shell OS X to
success.
5)	Do you need any kind of compatibility with PC/Mac/Linux/...?  Does
the machine have to have a graphics head or is it merely a server - the
latter is WAY easier to configure and maintain.  I'm not sure how PC's
communicate with
Mac/Linux/Unix, but the latter three seem to talk to each other well.
Hope this helps...
Joe

I've used various versions of Gaussian on various machines at supercomputing
centers for many years (at least 18 years).  My current favorite machine is
SGI's itantuim/altix machine.  It is shared memory so gaussian speed-up is
nearly linear (at least up to 8 processors, as many as I have tried), and
the 64 bit system makes file size limitations no longer an issue.  I have
been able to optimizations/frequency calculations on molecules with nearly
150 atoms, including Re atoms, using good quality DFT methods, as well as
MP2 calculations that choked other machines I have used.
Steve Williams

I hope that helps
Ian Hovell