Supermicro LE vs HE-SL chipsets

[Ray Muno]

I posed my question (CAS2 versus CAS3) to SuperMicro directly.  Here is 
their response:

"CL2 is always faster per spec, but I really do not believe you will see such
an increase with this motherboard simply because it uses 2 way memory
interleave which basically cuts your memory reads/writes in half.  Both
motherboard can run but CL2 and CL3, but I have not tested the performance
difference and our lab does not make this type of comparison.  Just by the
fact that they use interleave memory leads me to believe you will not see
great increase in performance since the interleave memory is not a bottle
neck the system. On system which use a single memory pool then yes you will
normally see an improvement.  Again I really do not believe you will here."

In any event, this still has not left me convinced whether CAS 2 will buy
us anything on an HE-SL board.  You indicate that it did on a LE based
board, the 370DLE.

I should actually have a 370DE6 and 370DER in my hands in the very near
future.  I have ordered CAS2 spec PC133 memory for them.  Hopefully we
will be able to come to some meanginful conclusion on this issue.  

The price between CAS2 and CAS3 spec memory is fairly insignificant. The
main issue is the availabilty of DIMMS in sizes other than 128 or 256 MB.

Many of the vendors claim that the majority of the memory they are currently
producing will meet the CAS2 spec even though they are selling it as CAS3.
What complicates this is that most of the newer boards seem to require that
the memory modules have the SPD (Serial Presence Detect) capability.  If
the module is being sold as CAS3, it is programmed to say that. Whether
or not you can override what is in the SPD module is unclear to me and I
would imagine it is motherboard/BIOS dependent.

We tested an ASUS CUSL2-C (815EP based) quite heavily.  We could set the 
board to CAS2 settings (2-2-2) memory and it would not boot with CAS3
memory installed.  By default, it gets its settings via SPD. With the
appropriate memory, everything was fine and we saw a tremendous increase
in performance.  For STREAM benchmarks, the board with PC133 memory, CAS3,
was slower than a BX board running PC100 memory.


On Fri, Jan 26, 2001 at 12:48:41PM -0600, Donald B. Kinghorn wrote:
> >
> > The BIOS allows you to twiddle with the CAS memory paramaters.  At this point,
> > we have not determined if CAS 2 versus CAS 3 memory makes any difference on
> > a ServerWorks based board.  Has anyone made this determination?  I would
> > love to hear feedback.
> 
> On the 370DLE motherboard we saw a nice speedup on our quantum chemistry codes when we tweaked all of the memory
> settings up a notch from the bios optimal defaults (cas3->cas2). This is with Micron cas2 pc133 256MB modules ...
> The results depend on how the jobs used memory and ranged from no improvement to over %12 improvement. ... So, your
> mileage may vary. Best thing to do is get a motherboard and some good quality memory and try it on the codes you
> want to run to see if the extra cost of the cas2 memory is worth it to you.
> 
> -Don
> 
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 Ray Muno                           http://www.aem.umn.edu/people/staff/muno
 University of Minnesota                          e-mail:   muno at aem.umn.edu
 Aerospace Engineering and Mechanics               Phone:     (612) 625-9531
 110 Union St. S.E.		                     FAX:     (612) 626-1558
 Minneapolis, Mn 55455			

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