Will my motherboard handle one matched pair of dual-channel memory and one non-matched stick?

Posted on 2006-04-28
Medium Priority
Last Modified: 2013-11-10
 I have a Dell PowerEdge 400SC.  It has four memory slots that accept sticks of up to 1GB DDR 333 or DDR 400.  I have confirmed the configuration of the slots.  There are two that are black and two that are white.  For Dual-channel to work properly I have to match the RAM sticks in conjunction with the colors.  Not a big deal.  Here is the issue though, and will make this a two part question, so more points...

  I had 2 matching 128mb sticks in it before along with one 512mb stick.  I purchased two matching 256mb modules (512mb total) thinking that the server had two matching 256mb sticks and one 128mb stick because it read 768mb.  So:

      My thoughts:                                  Actual:
      2 x 256mb DDR333                         2 x 128mb DDR333
      1 x 128mb DDR333                         1 x 512mb DDR333

  Then remember I bought two more 256 mb DDR400 sticks.  So my total modules is five.  My intention is was to upgrade to 1GB Dual-channel memory working in Dual-channel mode.  However, we can see by my diagram that I cannot do that now.  What I have done is put the two new 256mb DDR400 sticks in the correct dual channel slots.  If alone, they would be working in dual channel mode, I have confirmed this.  I have also put the existing 512mb stick in one of the unmatched dual-channel slots.  See below:

      Slot 1 (white):  512mb DDR333 ---------|
      Slot 2 (black):  256mb DDR400 ---|      |
      Slot 3 (white):  <Empty>       -----|-----|
      Slot 4 (black):  256mb DDR400----|

   My first question is:  Will this degrade or negate the performance of the correctly matched 256mb DDR400 sticks?  The Server booted and shows 1GB for memory.  But I'm concerned that I have lost the Dual-channel capability.

   Second Question is:  If the 512GB does negate the dual-channel of the 2 x 256mb sticks then which would be more efficient or faster:  a)  using the two original 128mb sticks in the white slots and the two new 256mb sticks in the black slots (768mb in dual-channel mode)?  or b)  sticking with the configuration i currently have running in what I would assume to be single channel mode if you have gotten this far in this question (1GB in single-channel mode)?

   I know it's a lot, but I hope my description has made it clear what I'm doing and what I'm looking to recieve for an answer.  Any questions, let me know.  Thank you

Question by:compsol1993
  • 3
LVL 53

Expert Comment

by:Will Szymkowski
ID: 16562077
Hello there,

The Ram in the machine is going to run at the slowest MHz so your going to be running at 333MHz for all of them.

Personally I would put the 128MB moduels back on the motherboard because even though you are losing 256MB you are also deminishing the speeds of your 256 Moduels and the 512MB is not running in Dual.

hope this helps
LVL 53

Accepted Solution

Will Szymkowski earned 2000 total points
ID: 16562103
Are your 128MB sticks running 400MHz or 333MHz? If they are 333MHz your best bet would to leave the 512MB.

Sorry didn't see what the MHz was for the 128 moduels

Author Comment

ID: 16562422
Yeah, the 128mb sticks are 333MHz
LVL 53

Expert Comment

by:Will Szymkowski
ID: 16562678
Yeah I would then leave the 512MB moduel in the motherboard.

Hope this helps
LVL 14

Expert Comment

ID: 16563094
Since you have independednt memory addressing the dual channel RAM will work in that same capacity. However if you put the 512 MB Ram in the 3rd slot you would be able to get better performance cause the 256 dual channel bank is gonna get used first. This would also mean that the windows kernel will rest in the faster 400 Mhz dual channel RAM giving better performance.

You can benchmark your system with both configs and see if there is any performance change.


This should help or try running any game and see if it makes a difference. You might wanna do this only if u like to squeeze out the most performance.




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