Xeon Memory Speed - 1DPC vs 2DPC

[idata]

In a description of the Xeon 5500 series processor, Intel states:

DIMMs with DDR3-1333 speed are allowed only when one DIMM Per Channel (1DPC) is populated. If two 1333 MT/s capable UDIMMs or RDIMMs are detected in the same channel, BIOS would flag this as a warning and force the speed to 1066 MT/s.

(http://www.intel.com/Assets/PDF/datasheet/321322.pdf http://www.intel.com/Assets/PDF/datasheet/321322.pdf)

Is this also true for the 3400 series processors, specifically the 3430?

Bob Simon

[DSilv11]

Xeon 5600 support 2 dimms per channal at 1333. Don't know obout the 3430

[Edward_Z_Intel]

Xeon 3400 series supports 2 DPC at 1333MHz, as per the http://www.intel.com/Assets/en_US/PDF/datasheet/322371.pdf Intel® Xeon® Processor 3400 Series Datasheet Volume 1, section 1.2.1.

[idata]

Edward,

Your reply is, of course, encouraging but I'm not sure I know how to correctly interpret table 1-1 in section 1.2.1 of the datasheet. For the 3420 chipset, the table says that 1 or 2 DIMMs are allowed per channel and that the transfer rate for DDR3 ECC Unbuffered DIMM is "1066, 1333".

Does this mean that the processor can access BOTH modules in the same channel at either 1066 or 1333 MT/s?

How does the processor determine what transfer rate to use?

Assuming that the Xeon 3400 processor series eliminates the 1066 MT/s restriction with 2 DIMMs/ch, do you have any insight as to why the 5500 has this restriction?

Thanks!

Bob

[Edward_Z_Intel]

Yes, the memory will run at the highest possible transfer rate.

The Xeon 5500 series has 1DPC 1333Mhz limitation. Xeon 3400 series and 5600 series can support 2DPC at 133Mhz. I believe that's because of the improvement of the integrated memory controller.

[DSilv11]

The system will detrermine memory speed based on BIOS control.

Basicly if all components report that they support 1333, the system sets the clock to 1333.

If you mix any components by installing a DIMM or a processor that only supports 1066, the entire bus will clock down to 1066, so check both your memory and processor spec. before buying.

The 5500 was the first QPI processor and the processor team desided to be safe rather than sorry when it came to 2DPC loading on the memory bus.

It is again under BIOS control and you may find some vendors that desided to brave it and allowed the 5500's to clock up to 1333 2DPC.

Intel server boards follow the processor recomendation and only allow 2DPC@1333 with the 5600.