KN8E-Dlx Look carefully at memory stick specifications

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aberger

My local Fry's was having a pretty good sale on 512 MB PC3200 memory
modules so I thought I would add one more to my machine, bringing my
memory capacity up to 1.5 GB. It seemed reasonable, I had 3 slots and
was currently using only two of them, one each for a 512 MB module.

Even though I was sure it should work I decided to RTFM before buying
the memory. The manual was most instructive. Seems that I can't use
three 512 MB modules and keep the speed at 400 MHz. In fact, the specs
in general are quite restrictive when it comes to running at 400MHz. It
makes sense when you think about general engineering problems of trying
to run at 400 MHz with the capacitive loading of the memory chips. Only
certain combinations keep the loads within reasonable bounds.

Anyway, if you are thinking of adding fast memory, check out the manual
before you buy.

Arnie
 
My local Fry's was having a pretty good sale on 512 MB PC3200 memory
modules so I thought I would add one more to my machine, bringing my
memory capacity up to 1.5 GB. It seemed reasonable, I had 3 slots and
was currently using only two of them, one each for a 512 MB module.

Even though I was sure it should work I decided to RTFM before buying
the memory. The manual was most instructive. Seems that I can't use
three 512 MB modules and keep the speed at 400 MHz. In fact, the specs
in general are quite restrictive when it comes to running at 400MHz. It
makes sense when you think about general engineering problems of trying
to run at 400 MHz with the capacitive loading of the memory chips. Only
certain combinations keep the loads within reasonable bounds.

Anyway, if you are thinking of adding fast memory, check out the manual
before you buy.

Arnie
Click to expand...

The info in the manual is based on page 16 of this:

http://web.archive.org/web/20031203...ent_type/white_papers_and_tech_docs/24659.PDF

That table of information applies to any S754 board.
Some motherboard makers print the table verbatim, while others
mess with it a bit. AMD has buried this info and you won't find
it on the site now. At least I cannot find it since they
repartitioned the Athlon64 docs. That is why I had to use
web.archive.org, to find it again.

The S939 also has restrictions. It has speed options DDR400/DDR333
and command rate 1T/2T, to adjust for load. I think I've read that
the BIOS downshifts to DDR333 when four DIMMs are present, and the
user has to set it back to DDR400. With four sticks, the 2T command
rate can be used to add stability, at the expense of perhaps 15-25%
less memory bandwidth. With two sticks, it is possible 1T command
rate will work. The S939 might be better off with 2x1GB than with
4x512MB, although that would be more expensive. If you go to 4x1GB,
that would likely be slower than 2x1GB (for the same reasons),
and you might not get to use all the memory due to address space
limitations. If you try to use 2x1GB and 2x512MB, that might disable
interleaving. I think the AMD controller has some interleaving
options, but I'm not sure to what extent the BIOS supports them -
the more "symmetric" the memory configuration is, like 4x512MB
or 4x1GB, the more likely an interleaving option would work.

"Memory interleaving mode can be used" Pg 78
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26094.PDF

Impact of command rate:
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2069&p=8

Board review of a S939 board - 4 DIMMs at DDR400 at Command Rate 2T
http://www.anandtech.com/mb/showdoc.aspx?i=2285&p=4

Paul
 
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