4gb (4 memory sticks) at 400Mhz on socket 939 MB -- JEDEC specifications ...

[Bryan J. Smith]

On Sat, 2006-07-08 at 13:22 -0500, Mohamad Al-Saqer wrote:
> Is it possible to find an AMD 64 socket 939 motherboard which supports 4 
> memory sticks of 4GB to run at max speed 400MHz? From some available MB 
> manuals the speed is either downgraded to 333MHz when 4 mem sticks are used 
> or there is no mention of the issue at all.

JEDEC specifications require that only one (1) DDR 200MHz
(DDR400/PC-3200) 64-bit DIMM be used per 64-bit channel (2x32-bit
banks), or two (2) for registered per 64-bit channel (4x32-bit banks).  

That means a maximum of (2) DDR DIMMs for unregistered Socket-939.
That means a maximum of (4) DDR DIMMs for registered Socket-940.

> From my search on google, some blame it on limitation of the motherboard 
> chipset. Others blame it on processors prior to the E revision. Nothing on 
> the net I came across would be a clear answer.

Hit many discussions on JEDEC DDR specifications.
Here's the rule ...

  DDR 100MHz (DDR200, PC1600)
    3 DIMMs/channel, 6 DIMMs for S939, 12 DIMMs for S940

  DDR 133/166MHz (DDR266/333, PC2100/2700)
    2 DIMMs/channel, 4 DIMMs for S939, 8 DIMMs for S940

  DDR 200MHz (DDR400, PC3200)
    1 DIMM/channel, 2 DIMMs for S939, 4 DIMMs for S940


> I would suspect that tyan K8E (and K8E-SLI) doesn't have this limitation, does 
> it? Because I saw at amd website some bechmarks on systems built on this 
> motherboard with 4GB installed. However no say on wether these system were 
> running at 400MHz FSB or less.
> I appreciate help and any clarification.

As above.

BTW, your greater concern than signaling is timing.  Slower timed DDR400
DIMMs often cause more of an impact that faster timed DDR333 DIMMs.

I personally use at least 2.5-3-3-6 for DDR400.

If you're using 3-3-3-8 or worse for DDR400, you might as well run at
DDR333.


-- 
Bryan J. Smith           Professional, technical annoyance
mailto:b.j.smith at ieee.org     http://thebs413.blogspot.com
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