"Jab" said:
Perhaps this is daft but I'd thought I would enquire anyway.
With the ASUS K8V-X board, which set-up is best to use:
[ NB: I have the 2x256MB PC3200 already ]
a) 1x1GB Pc3200 + 2x256MB Pc3200
b) 2x512MB Pc3200
c) 1x1GB Pc3200
Is there a problem with a) ?
Any help is appreciated!
Jonny
It depends on your definition of "best".
Most people would want a good combination of speed
and size for the memory. Download the PDF user manual
for the K8V-X and have a look at Table 1. It has various
combinations of single and double sided sticks. It would
seem the table for this board is not the standard one
issued by AMD (as AMD made the original version of this
table). The K8V-X table is more conservative than the average
"Table 1", as normally you can run two double sided DIMMs
at DDR400. (For example, download the manual for the
K8N-E Deluxe, and look at the Table 1 in there.)
The characteristics of the processor determine what
Table 1 looks like, not the motherboard. That is because
the memory controller is inside the processor. In the case
of an S754 processor, there are two address busses and
one data bus. The single data bus is what makes the processor
a "single channel" processor. One address bus is connected
to slot 1, and the other address bus is connected to slot
2 and slot 3. That is why Table 1 is so weird looking,
as the best configurations will be when the address bus
loading is "shared" between the two address busses.
Now, at the processor level, there are various steppings.
If I go to
www.amdcompare.com, and look at the processors
available for S754, I see that the Athlon64 processors are
still 130nm. Some of them are old enough, that they might
not even have a Command Rate setting in the BIOS, which
means the only user option is to drop the memory bus clock
rate. A Sempron in the list looked like it was based on
Rev.E, and potentially, that processor would have better
memory drive characteristics. It means selecting a processor
with the best processing characteristics, and best bus
driving characteristics, is a bit harder. (Sempron P.R.
ratings are slower than their Athlon64 counterparts.)
Look for section 1.4 "Register Differences in Revisions of
the AMD Athlon 64 and AMD Opteron Processors" in this
document. It mentions that Command Rate "Enable 2T" was
added to processor revision CG (or later steppings).
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26094.PDF
This document has a nice geneology table. Table 1. "CPUID
Values for Revisions of the Processors", using the third
column over, shows S754 processors are available in C0,
CG, and D0 steppings, and C0 is too old to support the
"Enable 2T" setting.
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/25759.PDF
If you go to
www.amdcompare.com and list the S754 processors,
there are rev.E Semprons listed (90 nm internal geometry),
but Semprons are lesser processors when compared to the
Athlon64 ones (the Sempron P.R. rating is comparable to an
Intel Celeron's clock speed equivalent). Amdcompare lists
some C0 stepping S754 processors, and I really have trouble
believing they would still be shipping those - in any case,
you want a CG or D0 stepping. Now, doc 25759 says there are
D0 S754 processors, but amdcompare doesn't show _any_ in their
list. Maybe all these sources of info are not up to date.
Returning to the memory config options that you listed:
I would pick (c) as the least risky configuration. It won't
matter what kind of processor drives it. DDR400 should not
be a problem.
Your option (b) is a bit tougher for the processor to drive.
Depending on which version of the Asus Table 1 you choose to
believe, it will run at either DDR400 or DDR333. If you have
a processor with an "Enable 2T" Command Rate setting, that
gives you another "knob" to twist, if the RAM is not stable.
Enabling 2T reduces RAM performance, but gives the address
more time to settle on the address busses.
Your option (a) is the heaviest loading case. Be prepared
to drop the memory clock to either DDR333 or DDR266,
depending on whether all three sticks are double sided or
not. For example, if you are doing Photoshop, and need
all the memory you could get, it would be better to use
3x1GB DIMMs and take the hit on memory bus speed, than
to use less memory, which would cause Photoshop to hit the
scratch disk more. For most day to day activities, a lot
of RAM is not going to be that useful, so the drop in
memory speed may be a poorer compromise.
Also, keep the memory performance thing in perspective,
as the Athlon64 has very good cache characteristics, and
doesn't suffer too much from a non-optimal memory config.
So, that is the view from the theoretical side of things.
Now, you'll need to visit the private forums, and see
what memory speeds real users have managed to squeeze from
their processors
Paul
