dual channel rules
 

Hi,

I have a question that is not really linux specific but, well, hardware is hardware isn't it?
The thing is I get a new motherboard (gigabyte) today and I was hoping to pair it with a heatsink I already had. Now it appears I was being too optimistic; the heatsink is huge enough to cover the first RAM slot, which leaves only two available if I am going to take advantage of dual channel. But it is the age of affordable 2GB dimms so I do not really mind (for now).
What puzzled me, though, is that the motherboard manual states that the first two slots should really be preferred over the next two, even though using the latter only appears to work, too. Now why that sort of recommendation? I re-checked the manual for an MSI board I have and that one goes even further: no dimm in slot1 == not boot! So are not all slots created equal? And why not?

Hi,

The way the dual channel memory is handled is restricted to the first two slot because of the design for the MB to allow access to the memory controller. The support of the channel addressing support chip to control the path is just designed for the two slots on most MB.

Because of the dual channel there is the address extension of the contiguous memory to have speedier access to the memory control chip thus preventing any bottlenecks when utilizing newer processors by providing dual channels of memory instead of a single channel.

You don't always have to match the memory but it is best if you do. Some manufactures design around the use of matched pairs. You can always step down your CPU clock then hope the unmatched pair will meet the processors needs at the cost of the processor speed.

Thanks for that information. Turns out the heatsink does fit only I now have a different problem. The thing is rated for only up to 89W. :rolleyes:

I assume you are using an AMD processor and you are stating TDP or Thermal Demand Power. This spec is very vague between AMD and Intel. Intel's TDP spec is vague for all of its processors while AMD is pretty consistent. AMD states TDP as "Thermal Design Power (TDP) is measured under the conditions of TCASE Max, IDD Max, and VDD=VID_VDD, and include all power dissipated on-die from VDD, VDDIO, VLDT, VTT, and VDDA." This means in laymen terms is basing on a constant voltage of processor and the current can not exceeded the total power handling of TDP. Basically it is the total heat index with out using a heat sink which is a worst case scenario.

This is taken from the following page.

http://www.silentpcreview.com/article169-page3.html

Intel's TDP is basically an average rating during use which is with or with out a heat sink.

In conclusion, AMD processors provides you all of its performance that you paid for while Intel is giving you less. Intel's TDP is average, but the amount of power could be more than this spec for a short amount of time. AMD gives you head room depending on the efficiency of the heat sink, but its maximum power will be about double or more with out causing too much damage.